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Hydrogen

HYDROGEN

CONCEPT

First element on the periodic table, hydrogen is truly in a class by itself. It does not belong to any family of elements, and though it is a nonmetal, it appears on the left side of the periodic table with the metals. The other elements with it in Group 1 form the alkali metal family, but obviously, hydrogen does not belong with them. Indeed, if there is any element similar to hydrogen in simplicity and abundance, it is the only other one on the first row, or period, of the periodic table: helium. Together, these two elements make up 99.9% of all known matter in the entire universe, because hydrogen atoms in stars fuse to create helium. Yet whereas helium is a noble gas, and therefore chemically unreactive, hydrogen bonds with all sorts of other elements. In one such variety of bond, with carbon, hydrogen forms the backbone for a vast collection of organic molecules, known as hydrocarbons and their derivatives. Bonded with oxygen, hydrogen forms the single most important compound on Earth, and the most important complex substance other than air: water. Yet when it bonds with sulfur, it creates toxic hydrogen sulfide; and on its own, hydrogen is extremely flammable. The only element whose isotopes have names, hydrogen has long been considered as a potential source of power and transportation: once upon a time for airships, later as a component in nuclear reactionsand, perhaps in the future, as a source of abundant clean energy.

HOW IT WORKS

The Essentials

The atomic number of hydrogen is 1, meaning that it has a single proton in its nucleus. With its single electron, hydrogen is the simplest element of all. Because it is such a basic elemental building block, figures for the mass of other elements were once based on hydrogen, but the standard today is set by 12C or carbon-12, the most common isotope of carbon.

Hydrogen has two stable isotopesforms of the element that differ in mass. The first of these, protium, is simply hydrogen in its most common form, with no neutrons in its nucleus. Protium (the name is only used to distinguish it from the other isotopes) accounts for 99.985% of all the hydrogen that appears in nature. The second stable isotope, deuterium, has one neutron, and makes up 0.015% of all hydrogen atoms. Tritium, hydrogen's one radioactive isotope, will be discussed below.

The fact that hydrogen's isotopes have separate names, whereas all other isotopes are designated merely by element name and mass number (for example, "carbon-12") says something about the prominence of hydrogen as an element. Not only is its atomic number 1, but in many ways, it is like the number 1 itselfthe essential piece from which all others are ultimately constructed. Indeed, nuclear fusion of hydrogen in the stars is the ultimate source for the 90-odd elements that occur in nature.

The mass of this number-one element is not, however, 1: it is 1.008 amu, reflecting the small quantities of deuterium, or "heavy hydrogen," present in a typical sample. A gas at ordinary temperatures, hydrogen turns to a liquid at 423.2°F (252.9°C), and to a solid at 434.°F (259.3°C). These figures are its boiling point and melting point respectively; only the figures for helium are lower. As noted earlier, these two elements make up all but 0.01% of the known elemental mass of the universe, and are the principal materials from which stars are formed.

Normally hydrogen is diatomic, meaning that its molecules are formed by two atoms. At the interior of a star, however, where the temperature is many millions of degrees, H2 molecules are separated into atoms, and these atoms become ionized. In other words, the electron separates from the proton, resulting in an ion with a positive charge, along with a free electron. The positive ions experience fusionthat is, their nuclei bond, releasing enormous amounts of energy as they form new elements.

Because the principal isotopic form of helium has two protons in the nucleus, it is natural that helium is the element usually formed; yet it is nonetheless trueamazing as it may seemthat all the elements found on Earth were once formed in stars. On Earth, however, hydrogen ranks ninth in its percentage of the planet's known elemental mass: just 0.87%. In the human body, on the other hand, it is third, after oxygen and carbon, making up 10% of human elemental body mass.

Hydrogen and Bonding

Having just one electron, hydrogen can bond to other atoms in one of two ways. The first option is to combine its electron with one from the atom of a nonmetallic element to make a covalent bond, in which the two electrons are shared. Hydrogen is unusual in this regard, because most atoms conform to the octet rule, ending up with eight valence electrons. The bonding behavior of hydrogen follows the duet rule, resulting in just two electrons for bonding.

Examples of this first type of bond include water (H2O), hydrogen sulfide (H2S), and ammonia (NH3), as well as the many organic compounds formed on a hydrogen-carbon backbone. But hydrogen can form a second type of bond, in which it gains an extra electron to become the negative ion H, or hydride. It is then able to combine with a metallic positive ion to form an ionic bond. Ionic hydrides are convenient sources of hydrogen gas: for instance, calcium hydride, or CaH2, is sold commercially, and provides a very convenient means of hydrogen generation. The hydrogen gas produced by the reaction of calcium hydride with water can be used to inflate life rafts.

The presence of hydrogen in certain types of molecules can also be a factor in intermolecular bonding. Intermolecular bonding is the attraction between molecules, as opposed to the bonding within molecules, which is usually what chemists mean when they talk about "bonding."

Hydrogen's Early History

Because it bonds so readily with other elements, hydrogen almost never appears in pure elemental form on Earth. Yet by the late fifteenth century, chemists recognized that by adding a metal to an acid, hydrogen was produced. Only in 1766, however, did English chemist and physicist Henry Cavendish (1731-1810) recognize hydrogen as a substance distinct from all other "airs," as gases then were called.

Seventeen years later, in 1783, French chemist Antoine Lavoisier (1743-1794) named the substance after two Greek words: hydro (water) and genes (born or formed). It was another two decades before English chemist John Dalton (1766-1844) formed his atomic theory of matter, and despite the great strides he made for science, Dalton remained convinced that hydrogen and oxygen in water formed "water atoms." Around the same time, however, Italian physicist Amedeo Avogadro (1776-1856) clarified the distinction between atoms and molecules, though this theory would not be generally accepted until the 1850s.

Contemporary to Dalton and Avogadro was Swedish chemist Jons Berzelius (1779-1848), who developed a system of comparing the mass of various atoms in relation to hydrogen. This method remained in use for more than a century, until the discovery of neutrons, protons, and isotopes pointed the way toward a means of making more accurate determinations of atomic mass. In 1931, American chemist and physicist Harold Urey (1893-1981) made the first separation of an isotope: deuterium, from ordinary water.

REAL-LIFE APPLICATIONS

Deuterium and Tritium

Designated as 2H, deuterium is a stable isotope, whereas tritium3His unstable, or radioactive. Not only do these two have names; they even have chemical symbols (D and T, respectively), as though they were elements on the periodic table. Just as hydrogen represents the most basic proton-electron combination against which other atoms are compared, these two are respectively the most basic isotope containing a single neutron, and the most basic radioisotope, or radioactive isotope.

Deuterium is sometimes called "heavy hydrogen," and its nucleus is called a deuteron. In separating deuteriuman achievement for which he won the 1934 Nobel PrizeUrey collected a relatively large sample of liquid hydrogen: 4.2 qt (4 l). He then allowed the liquid to evaporate very slowly, predicting that the more abundant protium would evaporate more quickly than the heavier isotope. When all but 0.034 oz (1 ml) of the sample had evaporated, he submitted the remainder to a form of analysis called spectroscopy, adding a burst of energy to the atoms and then analyzing the light spectrum they emitted for evidence of differing varieties of atoms.

With an atomic mass of 2.014102 amu, deuterium is almost exactly twice as heavy as protium, which has an atomic mass of 1.007825. Its melting points and boiling points, respectively 426°F (254°C) and 417°F (249°C), are higher than for protium. Often, deuterium is applied as a tracer, an atom or group of atoms whose participation in a chemical, physical, or biological reaction can be easily observed.

DEUTERIUM IN WAR AND PEACE.

In nuclear power plants, deuterium is combined with oxygen to form "heavy water" (D2O), which likewise has higher boiling and melting points than ordinary water. Heavy water is often used in nuclear fission reactors to slow down the fission process, or the splitting of atoms. Deuterium is also present in nuclear fusion, both on the Sun and in laboratories.

During the period shortly after World War II, physicists developed a means of duplicating the thermonuclear fusion process. The result was the hydrogen bombmore properly called a fusion bombwhose detonating device was a compound of lithium and deuterium called lithium deuteride. Vastly more powerful than the "atomic" (that is, fission) bombs dropped by the United States over Japan (Nagaski and Hiroshima) in 1945, the hydrogen bomb greatly increased the threat of worldwide nuclear annihilation in the postwar years.

Yet the power that could destroy the world also has the potential to provide safe, abundant fusion energy from power plantsa dream as yet unrealized. Physicists studying nuclear fusion are attempting several approaches, including a process involving the fusion of two deuterons. This fusion would result in a triton, the nucleus of tritium, along with a single proton. Theoretically, the triton and deuteron would then be fused to create a helium nucleus, resulting in the production of vast amounts of energy.

TRITIUM.

Whereas deuterium has a single neutron, tritiumas its mass number of 3 indicateshas two. And just as deuterium has approximately twice the mass of protium, tritium has about three times the mass, or 3.016 amu. Its melting and boiling points are higher still than those of deuterium: thus tritium heavy water (T2O) melts at 40°F (4.5°C), as compared with 32°F (0°C) for H2O.

Tritium has a half-life (the length of time it takes for half the radioisotopes in a sample to become stable) of 12.26 years. As it decays, its nucleus emits a low-energy beta particle, which is either an electron or a subatomic particle called a positron, resulting in the creation of the helium-3 isotope. Due to the low energy levels involved, the radioactive decay of tritium poses little danger to humans. In fact, there is always a small quantity of tritium in the atmosphere, and this quantity is constantly being replenished by cosmic rays.

Like deuterium, tritium is applied in nuclear fusion, but due to its scarcity, it is usually combined with deuterium. Sometimes it is released in small quantities into the groundwater as a means of monitoring subterranean water flow. It is also used as a tracer in biochemical processes, and as an ingredient in luminous paints.

Hydrogen and Oxygen

WATER.

Water, of course, is the most well-known compound involving hydrogen. Nonetheless, it is worthwhile to consider the interaction between hydrogen and oxygen, the two ingredients in water, which provides an interesting illustration of chemistry in action.

Chemically bonded as water, hydrogen and oxygen can put out any type of fire except an oil or electrical fire; as separate substances, however, hydrogen and oxygen are highly flammable. In an oxyhydrogen torch, the potentially explosive reaction between the two gases is controlled by a gradual feeding process, which produces combustion instead of the more violent explosion that sometimes occurs when hydrogen and oxygen come into contact.

HYDROGEN PEROXIDE.

Aside from water, another commonly used hydrogen-oxygen compound is hydrogen peroxide, or H2O2. A colorless liquid, hydrogen peroxide is chemically unstable (not "unstable" in the way that a radioisotope is), and decomposes slowly to form water and oxygen gas. In high concentrations, it can be used as rocket fuel.

By contrast, the hydrogen peroxide used in homes as a disinfectant and bleaching agent is only a 3% solution. The formation of oxygen gas molecules causes hydrogen peroxide to bubble, and this bubbling is quite rapid when the peroxide is placed on cuts, because the enzymes in blood act as a catalyst to speed up the reaction.

Hydrogen Chloride

Another significant compound involving hydrogen is hydrogen chloride, or HClin other words, one hydrogen atom bonded to chlorine, a member of the halogens family. Dissolved in water, it produces hydrochloric acid, used in laboratories for analyses involving other acids. Normally, hydrogen chloride is produced by the reaction of salt with sulfuric acid, though it can also be created by direct bonding of hydrogen and chlorine at temperatures above 428°F (250°C).

Hydrogen chloride and hydrochloric acid have numerous applications in metallurgy, as well as in the manufacture of pharmaceuticals, dyes, and synthetic rubber. They are used, for instance, in making pharmaceutical hydrochlorides, water-soluble drugs that dissolve when ingested. Other applications include the production of fertilizers, synthetic silk, paint pigments, soap, and numerous other products.

Not all hydrochloric acid is produced by industry, or by chemists in laboratories. Active volcanoes, as well as waters from volcanic mountain sources, contain traces of the acid. So, too, does the human body, which generates it during digestion. However, too much hydrochloric acid in the digestive system can cause the formation of gastric ulcers.

Hydrogen Sulfide

It may not be a pleasant subject, but hydrogenin the form of hydrogen sulfideis also present in intestinal gas. The fact that hydrogen sulfide is an extremely malodorous substance once again illustrates the strange things that happen when elements bond: neither hydrogen nor sulfur has any smell on its own, yet together they form an extremely noxiousand toxicsubstance.

Pockets of hydrogen sulfide occur in nature. If a person were to breathe the vapors for very long, it could be fatal, but usually, the foul odor keeps people away. The May 2001 National Geographic included two stories relating to such natural hydrogen-sulfide deposits, on opposite sides of the Earth, and in both cases the presence of these toxic fumes created interesting results.

In southern Mexico is a system of caves known as Villa Luz, through which run some 20 underground springs, many of them carrying large quantities of hydrogen sulfide. The National Geographic Society's team had to enter the caves wearing gas masks, yet the area teems with strange varieties of life. Among these are fish that are red from high concentrations of hemoglobin, or red blood cells. The creatures need this extra dose of hemoglobin, necessary to move oxygen through the body, in order to survive on the scant oxygen supplies. The waters of the cave are further populated by microorganisms that oxidize the hydrogen sulfide and turn it into sulfuric acid, which dissolves the rock walls and continually enlarges the cave.

Thousands of miles away, in the Black Sea, explorers supported by a grant from the National Geographic Society examined evidence suggesting that there indeed had been a great ancient flood in the area, much like the one depicted in the Bible. In their efforts, they had an unlikely ally: hydrogen sulfide, which had formed at the bottom of the sea, and was covered by dense layers of salt water. Because the Black Sea lacks the temperature differences that cause water to circulate from the bottom upward, the hydrogen sulfide stayed at the bottom.

Under normal circumstances, the wreck of a 1,500-year-old wooden ship would not have been preserved; but because oxygen could not reach the bottom of the Black Seaand thus wood-boring worms could not live in the toxic environmentthe ship was left undisturbed. Thanks to the presence of hydrogen sulfide, explorers were able to study the ship, the first fully intact ancient shipwreck to be discovered.

Hydrocarbons

Together with carbon, hydrogen forms a huge array of organic materials known as hydrocarbonschemical compounds whose molecules are made up of nothing but carbon and hydrogen atoms. Theoretically, there is no limit to the number of possible hydrocarbons. Not only does carbon form itself into seemingly limitless molecular shapes, but hydrogen is a particularly good partner. Because it has the smallest atom of any element on the periodic table, it can bond to one of carbon's valence electrons without getting in the way of the others.

Hydrocarbons may either be saturated or unsaturated. A saturated hydrocarbon is one in which the carbon atom is already bonded to four other atoms, and thus cannot bond to any others. In an unsaturated hydrocarbon, however, not all the valence electrons of the carbon atom are bonded to other atoms.

Hydrogenation is a term describing any chemical reaction in which hydrogen atoms are added to carbon multiple bonds. There are many applications of hydrogenation, but one that is particularly relevant to daily life involves its use in turning unsaturated hydrocarbons into saturated ones. When treated with hydrogen gas, unsaturated fats (fats are complex substances that involve hydrocarbons bonded to other molecules) become saturated fats, which are softer and more stable, and stand up better to the heat of frying. Many foods contain hydrogenated vegetable oil; however, saturated fats have been linked with a rise in blood cholesterol levelsand with an increased risk of heart disease.

PETROCHEMICALS AND FUNCTIONAL GROUPS.

One important variety of hydrocarbons is described under the collective heading of petrochemicalsthat is, derivatives of petroleum. These include natural gas; petroleum ether, a solvent; naphtha, a solvent (for example, paint thinner); gasoline; kerosene; fuel for heating and diesel fuel; lubricating oils; petroleum jelly; paraffin wax; and pitch, or tar. A host of other organic chemicals, including various drugs, plastics, paints, adhesives, fibers, detergents, synthetic rubber, and agricultural chemicals, owe their existence to petrochemicals.

Then there are the many hydrocarbon derivatives formed by the bonding of hydrocarbons to various functional groupsbroad arrays of molecule types involving other elements. Among these are alcoholsboth ethanol (the alcohol in beer and other drinks) and methanol, used in adhesives, fibers, and plastics, and as a fuel. Other functional groups include aldehydes, ketones, carboxylic acids, and esters. Products of these functional groups range from aspirin to butyric acid, which is in part responsible for the smell both of rancid butter and human sweat. Hydrocarbons also form the basis for polymer plastics such as Nylon and Teflon.

Hydrogen for Transportation and Power

We have already seen that hydrogen is a component of petroleum, and that hydrogen is used in creating nuclear powerboth deadly and peaceful varieties. But hydrogen has been applied in many other ways in the transportation and power industries.

There are only three gases practical for lifting a balloon: hydrogen, helium, and hot air. Each is much less dense than ordinary air, and this gives them their buoyancy. Because hydrogen is the lightest known gas and is relatively cheap to produce, it initially seemed the ideal choice, particularly for airships, which made their debut near the end of the nineteenth century.

For a few decades in the early twentieth century, airships were widely used, first in warfare and later as the equivalent of luxury liners in the skies. One of the greatest such craft was Germany's Hindenburg, which used hydrogen to provide buoyancy. Then, on May 6, 1937, the Hindenburg caught fire while mooring at Lakehurst, New Jersey, and 36 people were killeda tragic and dramatic event that effectively ended the use of hydrogen in airships.

Adding to the pathos of the Hindenburg crash was the voice of radio announcer Herb Morrison, whose audio report has become a classic of radio history. Morrison had come to Lakehurst to report on the landing of the famous airship, but ended up with the biggestand most horrifyingstory of his career. As the ship burst into flames, Morrison's voice broke, and he uttered words that have become famous:"Oh, the humanity!"

Half a century later, a hydrogen-related disaster destroyed a craft much more sophisticated than the Hindenburg, and this time, the medium of television provided an entire nation with a view of the ensuing horror. The event was the explosion of the space shuttle Challenger on January 28, 1986, and the cause was the failure of a rubber seal in the shuttle's fuel tanks. As a result, hydrogen gas flooded out of the craft and straight into the jet of flame behind the rocket. All seven astronauts aboard were killed.

THE FUTURE OF HYDROGEN POWER.

Despite the misfortunes that have occurred as a result of hydrogen's high flammability, the element nonetheless holds out the promise of cheap, safe power. Just as it made possible the fusion, or hydrogen, bombwhich fortunately has never been dropped in wartime, but is estimated to be many hundreds of times more lethal than the fission bombs dropped on Japanhydrogen may be the key to the harnessing of nuclear fusion, which could make possible almost unlimited power.

A number of individuals and agencies advocate another form of hydrogen power, created by the controlled burning of hydrogen in air. Not only is hydrogen an incredibly clean fuel, producing no by-products other than water vapor, it is available in vast quantities from water. In order to separate it from the oxygen atoms, electrolysis would have to be appliedand this is one of the challenges that must be addressed before hydrogen fuel can become a reality.

Electrolysis requires enormous amounts of electricity, which would have to be produced before the benefits of hydrogen fuel could be realized. Furthermore, though the burning of hydrogen could be controlled, there are the dangers associated with transporting it across country in pipelines. Nonetheless, a number of advocacy groupssome of whose Web sites are listed belowcontinue to promote efforts toward realizing the dream of nonpolluting, virtually limitless, fuel.

WHERE TO LEARN MORE

American Hydrogen Association (Web site). <http://www.clean-air.org> (June 1, 2001).

Blashfield, Jean F. Hydrogen. Austin, TX: Raintree Steck-Vaughn, 1999.

Farndon, John. Hydrogen. New York: Benchmark Books, 2001.

"Hydrogen" (Web site). <http://pearl1.lanl.gov/periodic/elements/1.html> (June 1, 2001).

Hydrogen Energy Center (Web site). <http://www.h2eco.org/> (June 1, 2001).

Hydrogen Information Network (Web site). <http://www.eren.doe.gov/hydrogen/> (June 1, 2001).

Knapp, Brian J. Carbon Chemistry. Illustrated by David Woodroffe. Danbury, CT: Grolier Educational, 1998.

Knapp, Brian J. Elements. Illustrated by David Woodroffe and David Hardy. Danbury, CT: Grolier Educational, 1996.

National Hydrogen Association (Web site). <http://www.ttcorp.com/nha/> (June 1, 2001).

Uehling, Mark. The Story of Hydrogen. New York: Franklin Watts, 1995.

KEY TERMS

COVALENT BONDING:

A type of chemical bonding in which two atoms share valence electrons.

DIATOMIC:

A term describing an element that exists as molecules composed of two atoms.

DUET RULE:

A term describing the distribution of valence electrons when hydrogen atomswhich end up with only two valence electronsexperience chemical bonding with other atoms. Most other elements follow the octet rule.

ELECTROLYSIS:

The use of an electric current to cause a chemical reaction.

FISSION:

A nuclear reaction involving the splitting of atoms.

FUSION:

A nuclear reaction that involves the joining of atomic nuclei.

HYDROCARBON:

Any chemical compound whose molecules are made up of nothing but carbon and hydrogen atoms.

HYDROGENATION:

A chemical reaction in which hydrogen atoms are added to carbon multiple bonds, as in a hydrocarbon.

ION:

An atom or group of atoms that has lost or gained one or more electrons, and thus has a net electrical charge.

IONIC BONDING:

A form of chemical bonding that results from attractions between ions with opposite electric charges. The bonding of a metal to a nonmetal such as hydrogen is ionic.

ISOTOPES:

Atoms that have an equal number of protons, and hence are of the same element, but differ in their number of neutrons. This results in a difference of mass. An isotope may either be stable or radioactive.

NUCLEUS:

The center of an atom, a region where protons and neutrons are located, and around which electrons spin. The plural of "nucleus" is nuclei.

OCTET RULE:

A term describing the distribution of valence electrons that takes place in chemical bonding for most elements, which end up with eight valence electrons. Hydrogen is an exception, and follows the duet rule.

ORGANIC:

At one time, chemists used the term "organic" only in reference to living things. Now the word is applied to most compounds containing carbon, with the exception of calcium carbonate (lime-stone) and oxides such as carbon dioxide.

RADIOISOTOPE:

An isotope subject to the decay associated with radioactivity. A radioisotope is thus an unstable isotope.

SATURATED:

A term describing a hydrocarbon in which each carbon is already bound to four other atoms.

TRACER:

An atom or group of atoms whose participation in a chemical, physical, or biological reaction can be easilyobserved. Radioisotopes are often used astracers.

UNSATURATED:

A term describing a hydrocarbon, in which the carbons involved in a multiple bond are free to bond with other atoms.

VALENCE ELECTRONS:

Electrons that occupy the highest principal energy level in an atom. These are the electrons involved in chemical bonding.

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Hydrogen (revised)

HYDROGEN (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Hydrogen is the most abundant element in the universe. Nearly nine out of every ten atoms in the universe are hydrogen atoms. Hydrogen is also common on the Earth. It is the third most abundant element after oxygen and silicon. About 15 percent of all the atoms found on the Earth are hydrogen atoms.

Hydrogen is also the simplest of all elements. Its atoms consist (usually) of one proton and one electron.

Hydrogen was first discovered in 1766 by English chemist and physicist Henry Cavendish (1731-1810). Cavendish was also the first person to prove that water is a compound of hydrogen and oxygen.

Some experts believe that hydrogen forms more compounds than any other element. These compounds include water, sucrose (table sugar), alcohols, vinegar (acetic acid), household lye (sodium hydroxide), drugs, fibers, dyes, plastics, and fuels.

SYMBOL
H

ATOMIC NUMBER
1

ATOMIC MASS
1.00794

FAMILY
Group 1 (IA)

PRONUNCIATION
HY-dru-jin

Discovery and naming

Hydrogen was probably "discovered" many times. Many early chemists reported finding a "flammable gas" in some of their experiments. In 1671, for example, English chemist Robert Boyle (1627-91) described experiments in which he added iron to hydrochloric acid (HCl) and sulfuric acid (H2SO4). In both cases, a gas that burned easily with a pale blue flame was produced.

The problem with these early discoveries was that chemists did not understand the nature of gases very well. They had not learned that there are many kinds of gases. They thought that all the "gases" they saw were some form of air with impurities in it.

Cavendish discovered hydrogen in experiments like those that Boyle performed. He added iron metal to different acids and found that a flammable gas was produced. But Cavendish thought the flammable gas came from the iron and not from the acid. Chemists later showed that iron is an element and does not contain hydrogen or anything else. Therefore, the hydrogen in Cavendish's experiment came from the acid:

Hydrogen was named by French chemist Antoine-Laurent Lavoisier (1743-94). Lavoisier is sometimes called the father of modern chemistry because of his many contributions to the science. Lavoisier suggested the name hydrogen after the Greek word for "water former" (that which forms water). (See sidebar on Lavoisier in the oxygen entry in volume 2.)

Physical properties

Hydrogen is a colorless, odorless, tasteless gas. Its density is the lowest of any chemical element, 0.08999 grams per liter. By comparison, a liter of air weighs 1.29 grams, 14 times as much as a liter of hydrogen.

Hydrogen changes from a gas to a liquid at a temperature of -252.77°C (-422.99°F) and from a liquid to a solid at a temperature of -259.2°C (-434.6°F). It is slightly soluble in water, alcohol, and a few other common liquids.

Chemical properties

Hydrogen burns in air or oxygen to produce water:

It also combines readily with other non-metals, such as sulfur, phosphorus, and the halogens. The halogens are the elements that make up Group 17 (VIIA) of the periodic table. They include fluorine, chlorine, bromine, iodine, and astatine. As an example:

Occurrence in nature

Hydrogen occurs throughout the universe in two forms. First, it occurs in stars. Stars use hydrogen as a fuel with which to produce energy. The process by which stars use hydrogen is known as fusion. Fusion is the process by which two or more small atoms are pushed together to make one large atom. In most stars, the primary fusion reaction that occurs is:

This equation shows that four hydrogen atoms are squeezed together (fused) to make one helium atom. In this process, enormous amounts of energy are released in the form of heat and light.

Hydrogen also occurs in the "empty" spaces between stars. At one time, scientists thought that this space was really empty, that it contained no atoms of any kind. But, in fact, this interstellar space (space between stars) contains a small number of atoms, most of which are hydrogen atoms. A cubic mile of interstellar space usually contains no more than a handful of hydrogen and other atoms.

Hydrogen occurs on the Earth primarily in the form of water. Every molecule of water (H2O) contains two hydrogen atoms and one oxygen atom. Hydrogen is also found in many rocks and minerals. Its abundance is estimated to be about 1,500 parts per million. That makes hydrogen the tenth most abundant element in the Earth's crust.

Hydrogen also occurs to a very small extent in the Earth's atmosphere. Its abundance there is estimated to be about0.000055 percent. Hydrogen is not abundant in the atmosphere because it has such a low density. The Earth's gravity is not able to hold on to hydrogen atoms very well. They float away into outer space very easily. Most of the hydrogen that was once in the atmosphere has now escaped into outer space.

Isotopes

There are three isotopes of hydrogen, hydrogen-1, hydrogen-2, and hydrogen-3. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

The three isotopes of hydrogen have special names. Hydrogen-1 is sometimes called protium. It is the simplest and most common form of hydrogen. Protium atoms all contain one proton and one electron. About 99.9844 percent of the hydrogen in nature is protium.

The man who gave hydrogen its name, Antoine-Laurent Lavoisier, is sometimes called the father of modern chemistry.

Hydrogen-2 is known as deuterium. A deuterium atom contains one proton, one electron, and one neutron. About 0.0156 percent of the hydrogen in nature is deuterium.

The third isotope of hydrogen, hydrogen-3, is tritium. An atom of tritium contains one proton, one electron, and two neutrons. There are only very small traces of tritium in nature.

Tritium is a radioactive isotope. A radioactive isotope is one that breaks apart and gives off some form of radiation. Some radioactive isotopes (such as tritium) occur in nature. They can also be produced in the laboratory. Very small particles are fired at atoms. These particles stick in the atoms and make them radioactive. Tritium is a widely used isotope and is now made in large amounts in the laboratory.

Tritium is widely used as a tracer in both industry and research. A tracer is a radioactive isotope whose presence in a system can easily be detected. The isotope is injected into the system at some point. Inside the system, the isotope gives off radiation. That radiation can be followed by means of detectors placed around the system.

Tritium is popular as a tracer because hydrogen occurs in so many different compounds. For example, suppose a scientist wants to trace the movement of water through soil. The scientist can make up a sample of water made with tritium instead of protium. As that water moves through the soil, its path can be followed by means of the radioactivity the tritium gives off.

Tritium is also used in the manufacture of fusion bombs. A fusion bomb is also known as a hydrogen bomb. In a fusion bomb, small atoms are squeezed together (fused) to make a larger atom. In the process, enormous amounts of energy are given off. For example, the first fusion bomb tested by the United States in 1952 had the explosive power of 15 million tons of TNT. A type of fusion bomb fuses tritium with deuterium to make helium atoms:

Stars use hydrogen as a fuel with which to produce energy.

Extraction

The obvious source for hydrogen is water. The Earth has enough water to supply people's need for hydrogen. The problem is that it takes a lot of energy to split a water molecule:

In fact, it simply costs too much to make hydrogen by this method. The cost of electricity is too high. So it is not economical to make hydrogen by splitting water.

A number of other methods can be used to produce hydrogen, however. For example, steam can be passed over hot charcoal (nearly pure carbon):

The same reaction can be used with steam and other carbon compounds. For example, using methane, or natural gas (CH4), the reaction is:

Hydrogen can also be made by the reaction between carbon monoxide (CO) and steam:

Because hydrogen is such an important element, many other methods for producing it have been invented. However, the preceding methods are the least expensive.

Uses

The most important single use of hydrogen is in the manufacture of ammonia (NH3). Ammonia is made by combining hydrogen and nitrogen at high pressure and temperature in the presence of a catalyst. A catalyst is a substance used to speed up or slow down a chemical reaction. The catalyst does not undergo any change during the reaction:

Ammonia is a very important compound. It is used in making many products, the most important of which is fertilizer.

Hydrogen is also used for a number of similar reactions. For example, it can be combined with carbon monoxide to make methanolmethyl alcohol, or wood alcohol (CH3OH):

Tritium (hydrogen-3, the third isotope of hydrogen), is used in the manufacture of fusion bombs.

Like ammonia, methanol has a great many practical uses in a variety of industries. The most important use of methanol is in the manufacture of other chemicals, such as those from which plastics are made. Small amounts are used as additives to gasoline to reduce the amount of pollution released to the environment. Methanol is also used widely as a solvent (to dissolve other materials) in industry.

Another important use of hydrogen is in the production of pure metals. Hydrogen gas is passed over a hot metal oxide to produce the pure metal. For example, molybdenum can be prepared by passing hydrogen over hot molybdenum oxide:

The Hindenburg explosion

T he Hindenburg was Germany's largest passenger airship. It was built in 1936 as a luxury liner, and made the trip to the United States faster than an ocean liner.

The Hindenburg was designed to be filled with helium, a safer gas than the highly flammable hydrogen. But in those post-World War II days, the United States suspected that Germany's new leader, Adolf Hitler (1889-1945), had military plans for helium-filled ships. So the United States refused to sell helium to the Zeppelin air-ship company. Seven million cubic feet of hydrogen was used instead. This made the crew very nervous about the potential for fire. Passengers were even checked for matches as they boarded!

On May 3, 1937, the Hindenburg left Frankfurt, Germany, for Lakehurst, New Jersey. It travelled over the Netherlands, down the English Channel, through Canada, and into the United States. Bad weather forced the ship to slow down several times, lengthening the trip. But it finally approached the field in Lakehurst around 7:00 P.M. on May 6.

After several minutes of maneuvers due to rain and wind, crewmen dropped ropes to the ground at 7:21. The ship was 200 feet above ground. Four minutes later, a small flame emerged on the skin of the ship, and crewmen heard a pop and felt a shudder. Seconds later, the Hindenburg exploded. Flaming hydrogen blasted out of the top. Within 32 seconds, the entire airship had burned, the framework had collapsed, and the entire ship lay smoldering on the ground. Thirty-six people died. Amazingly, 62 survived.

Although claims of sabotage have always surrounded the Hindenburg tragedy, American and German investigators both agreed it was an accident. Both sides concluded that the airship's hydrogen was ignited probably by some type of atmospheric electric discharge. Witnesses had noticed some of the skin of the ship flapping; they also observed the nose of the ship rise suddenly. Both indicate the likelihood that free hydrogen had escaped. The Hindenburg disaster ended lighter-than-air air-ship travel for many decades.

Hydrogenation is an important procedure to the food industry. In hydrogenation, hydrogen is chemically added to another substance. The reaction between carbon monoxide and hydrogen is an example of hydrogenation. Liquid oils are often hydrogenated. Hydrogenation changes the liquid oil to a solid fat. Most kitchens contain foods with hydrogenated or partially hydrogenated oils. Vegetable shortening, such as Crisco, is a good example. Hydrogenation makes it easier to pack and transport oils.

Hydrogen is also used in oxyhydrogen ("oxygen + hydrogen") and atomic hydrogen torches. These torches produce temperatures of a few thousand degrees. At these temperatures, it is possible to cut through steel and most other metals. These torches can also be used to weld (join together with heat) two metals.

Another use for hydrogen is in Lighter-than-air balloons. Hydrogen is the least dense of all gases. So a balloon filled with hydrogen can lift very large loads. Such balloons are not used to carry people. The danger of fire or explosion is too great. On May 6, 1937, a hydrogen fire destroyed the German airship Hindenburg, as it was landing in Lakehurst, New Jersey; 36 people died. Today, hydrogen balloons are used for lifting weather instruments into the upper atmosphere.

One of the best known uses of hydrogen is as a rocket fuel. Many rockets obtain the power they need for lift-off by burning oxygen and hydrogen in a closed tank. The energy produced by this reaction provides thrust to the rocket.

Solving the world's energy problems

M ost people don't worry about filling their cars with gas. They seem to believe that there will always be enough coal, oil, and natural gas to keep civilization running. Those three fuelsthe "fossil fuels"are what keep people on the move today. They fuel cars and trucks, heat homes and offices, and keep factories operating.

But fossil fuels will not last forever. At some point, all the coal, oil, and natural gas will be gone. What source of energy will humans turn to?

Some people believe that hydrogen is the answer. They talk about the day when the age of fossil fuels will be replaced by a hydrogen economy.

"Hydrogen economy" refers to a world in which the burning of hydrogen will be the main source of energy and power. Hydrogen seems to be a good choice for future energy needs. When it burns, it produces only water:

A lot of energy is produced in this reaction. That energy can be used to operate cars, trucks, trains, boats, and airplanes. It can be used as a source of heat for keeping people warm and running chemical reactions.

Why doesn't a hydrogen economy exist today? The answer is easy. It is still too expensive to make hydrogen gas. No one has found a way to remove hydrogen from water or some other source at a low cost. It is still cheaper to mine for coal or drill for oil than to make hydrogen.

But that may not always be true. Some day, someone will find a way to make hydrogen cheaply. When that happens, the day of the hydrogen economy will have arrived.

Compounds

Millions of hydrogen compounds are known. One of the most important groups of hydrogen compounds is the acids. An acid is any compound that contains hydrogen as its positive part. Common acids include: hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), acetic acid (HC2H3O2), phosphoric acid (H3PO4), and hydrofluoric acid (HF).

Acids are present in thousands of natural substances and artificial products. The following list gives a few examples: vinegar, or acetic acid (HC2H3O2); sour milk, or lactic acid (C3H6O3); lemons and other citrus fruits, or citric acid (C6H8O7); soda water, or carbonic acid (H2CO3); battery acid, or sulfuric acid H2SO4); and boric acid (H3BO3).

Health effects

Hydrogen is essential to every plant and animal. Nearly every compound in a living cell contains hydrogen. It is harmless to humans unless taken in very large amounts. In this case, it is dangerous only because it cuts off the supply of oxygen humans need to breathe.

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hydrogen

hydrogen (hī´drəjən) [Gr.,=water forming], gaseous chemical element; symbol H; at. no. 1; interval in which at. wt. ranges 1.00784–1.00811; m.p. -259.14°C; b.p. -252.87°C; density 0.08988 grams per liter at STP; valence usually +1.

The Isotopes and Forms

Atmospheric hydrogen is a mixture of three isotopes. The most common is called protium (mass no. 1, atomic mass 1.007822); the protium nucleus (protium ion) is a proton. A second isotope of hydrogen is deuterium (mass no. 2, atomic mass 2.0140), the so-called heavy hydrogen, often represented in chemical formulas by the symbol D. The deuterium nucleus, or ion, is called the deuteron; it consists of a proton plus a neutron. The two isotopes are found in atmospheric hydrogen in the proportion of about 1 atom of deuterium to every 6,700 atoms of protium. Protium and deuterium differ slightly in their chemical and physical properties; for example, the boiling point of deuterium is about 3°C lower than protium. The properties of compounds they form differ depending on the ratio of the two isotopes present.

Deuterium oxide (D2O), the so-called heavy water, is present in ordinary water; the concentration of deuterium oxide is increased by electrolysis of the water. The melting point (3.79°C), boiling point (101.4°C), and specific gravity (1.107 at 25°C) of deuterium oxide are higher than those of ordinary water. Deuterium oxide is used as a moderator in nuclear reactors. Deuterium is also of importance because of the wide use it has found in scientific research; for example, chemical reaction mechanisms have been studied by the use of deuterium atoms as tracers (i.e., deuterium is substituted for atoms of ordinary hydrogen in compounds), making it possible to follow the course of individual molecules in a reaction.

Tritium (mass no. 3, atomic mass 3.016), a third hydrogen isotope, is a radioactive gas with a half-life of about 121/4 years; it is often represented in chemical formulas by the symbol T. It is produced in nuclear reactors and occurs to a very limited extent in atmospheric hydrogen. It is used in the hydrogen bomb, in luminous paints, and as a tracer. The tritium nucleus, or ion, is called the triton; it consists of a proton plus two neutrons. Tritium oxide (T2O) has a melting point (4.49°C) higher than that of deuterium oxide.

Besides being a mixture of three isotopes, hydrogen is a mixture of two forms, an ortho form and a para form, which differ in their electronic and nuclear spins. At room temperature atmospheric hydrogen is about 3/4ortho-hydrogen and 1/4para-hydrogen. The two forms differ slightly in their physical properties.

Properties

Under ordinary conditions hydrogen is a colorless, odorless, tasteless gas that is only slightly soluble in water; it is the least dense gas known. It is the first element in Group 1 of the periodic table. Ordinary hydrogen gas is made up of diatomic molecules (H2) that react with oxygen to form water (H2O) and hydrogen peroxide (H2O2), usually as a result of combustion. A jet of hydrogen burns in air with a very hot blue flame. The flame produced by a mixture of oxygen and hydrogen gases (as in the oxyhydrogen blowpipe) is extremely hot and is used in welding and to melt quartz and certain glasses. Hydrogen gas must be used with caution because it is highly flammable; it forms easily ignited explosive mixtures with oxygen or with air (because of the oxygen in the air). At high temperatures hydrogen is a chemically active mixture of monohydrogen (atomic hydrogen) and the normal diatomic hydrogen (see allotropy).

Hydrogen has a great affinity for oxygen and is a powerful reducing agent (see oxidation and reduction). It reacts with nitrogen to form ammonia. With the halogens it forms compounds (hydrogen halides) that are strongly acidic in water solution. With sulfur it forms hydrogen sulfide (H2S), a colorless gas with an odor like rotten eggs; with sulfur and oxygen it forms sulfuric acid. It combines with several metals to form metal hydrides such as calcium hydride. Combined with carbon (and usually other elements) it is a constituent of a great many organic compounds, such as hydrocarbons, carbohydrates, fats, oils, proteins, and organic acids and bases.

It is theoretically possible for hydrogen to exhibit the properties of a metal, such as electrical conductivity. Although researchers have been able to squeeze hydrogen into liquid and crystalline solid states through applications of intense heat, cold, and pressure, the metallic form eluded them until 1996. By compressing liquid hydrogen to nearly 2 million atmospheres pressure and a temperature of 4,400°K, a team at the Lawrence Livermore National Laboratory created metallic hydrogen for a millionth of a second. While there is no practical application for the accomplishment, proof of the existence of a metallic form of hydrogen may have implications for theories of how Jupiter's magnetic field is produced.

Sources and Commercial Preparation

While hydrogen is only about one part per million in the atmosphere, it is the most abundant element in the universe. It is believed that hydrogen makes up about three quarters of the mass of the universe, or over 90% of the molecules. It is found in the sun and in other stars, where it is the major fuel in the fusion reactions (see nucleosynthesis) from which stars derive their energy.

Hydrogen is prepared commercially by catalytic reaction of steam with hydrocarbons, by the reaction of steam with hot coke (carbon), by the electrolysis of water, and by the reaction of mineral acids on metals. Millions of cubic feet of hydrogen gas are produced daily in the United States alone.

Uses

Hydrogen was formerly used for filling balloons, airships, and other lighter-than-air craft, a dangerous practice because of hydrogen's explosive flammability; there were disastrous fires, e.g., the immolation of the German airship Hindenburg at its mooring at Lakehurst, N.J., in 1937. Helium is preferable for use in lighter-than-air craft since it is not flammable. Hydrogen is used in the Haber process for the fixation of atmospheric nitrogen, in the production of methanol, and in hydrogenation of fats and oils. It is also important in low-temperature research. It can be liquefied under pressure and cooled; when the pressure is released, rapid evaporation takes place and some of the hydrogen solidifies.

Discovery of Hydrogen and Its Isotopes

Although hydrogen was prepared many years earlier, it was first recognized as a substance distinct from other flammable gases in 1766 by Henry Cavendish, who is credited with its discovery; it was named by A. L. Lavoisier in 1783. Deuterium was discovered by H. C. Urey, F. G. Brickwedde, and G. M. Murphy in 1932, although its existence had been suspected for some years. Deuterium oxide was also discovered by Urey and was first obtained in nearly pure form by G. N. Lewis. Tritium was synthesized by Ernest Rutherford, L. E. Oliphant, and Paul Harteck in 1935.

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Hydrogen

Hydrogen

Hydrogen is the simplest of all chemical elements. It is a colorless, odorless, tasteless gas that burns in air to produce water. It has one of the lowest boiling points, 252.9°C (423.2°F), and freezing points, 259.3°C (434.7°F), of all elements.

An atom of hydrogen contains one proton and one electron, making it the simplest atom that can be constructed. Because of the one proton in its nucleus, hydrogen is assigned an atomic number of 1. A total of three isotopes of hydrogen exist. Isotopes are forms of an element with the same atomic number but different atomic masses. Protium and deuterium are both stable isotopes, but tritium is radioactive.

Hydrogen is the first element in the periodic table. Its box is situated at the top of Group 1 in the periodic table, but it is not generally considered a member of the alkali family, the other elements that make up Group 1. Its chemical properties are unique among the elements, and it is usually considered to be in a family of its own.

The Hydrogen Economy

Some social scientists have called the last century of human history the Fossil Age. That term comes from the fact that humans have relied so heavily on the fossil fuelscoal, oil, and natural gasfor the energy we need to run our societies. What happens when the fossil fuels are exhausted? Where will humans turn for a new supply of energy?

A new generation of scientists is suggesting the use of hydrogen as a future energy source. Hydrogen burns in air or oxygen with a very hot flame that can be used to generate steam, electricity, and other forms of energy. The only product of that reaction is water, a harmless substance that can be released to the environment without danger. In addition, enormous amounts of hydrogen are available from water. Electrolysis can be used to obtain hydrogen from the world's lakes and oceans.

An economy based on hydrogen rather than the fossil fuels faces some serious problems, however. First, hydrogen is a difficult gas with which to work. It catches fire easily and, under certain circumstances, does so explosively. Also, the cost of producing hydrogen by electrolysis is currently much too high to make the gas a useful fuel for everyday purposes.

Of course, once the fossil fuels are no longer available, humans may have no choice but to solve these problems in order to remain a high-energy-use civilization.

History

Hydrogen was discovered in 1766 by English chemist and physicist Henry Cavendish (17311810). It was named by French chemist Antoine-Laurent Lavoisier (17431794) from the Greek words for "water-former." Early research on hydrogen was instrumental in revealing the true nature of oxidation (burning) and, therefore, was an important first step in the birth of modern chemistry.

Abundance

Hydrogen is by far the most abundant element in the universe. It makes up about 93 percent of all atoms in the universe and about three-quarters of the total mass of the universe. Hydrogen occurs both within stars and in the interstellar space (the space between stars). Within stars, hydrogen is consumed in nuclear reactions by which stars generate their energy.

Hydrogen is much less common as an element on Earth. Its density is so low that it long ago escaped from Earth's gravitational attraction. Hydrogen does occur on Earth in a number of compounds, however, most prominently in water. Water is the most abundant compound on Earth's surface.

Hydrogen also occurs in nearly all organic compounds and constitutes about 61 percent of all the atoms found in the human body. Chemists now believe that hydrogen forms more compounds than any other element, including carbon.

The Isotopes of Hydrogen

Atomic Atomic Percent of
Name Nucleus Number Mass Hydrogen Atoms
Protium 1 proton 1 1 99.985
Deuterium 1 proton; 1 neutron 1 2 0.015
Tritium 1 proton; 2 neutrons 3 trace

Properties and uses

Hydrogen is a relatively inactive element at room temperature, but it becomes much more active at higher temperatures. For example, it burns in air or pure oxygen with a pale blue, almost invisible flame. It can also be made to react with most elements, both metals and nonmetals. When combined with metals, the compounds formed are called hydrides. Some familiar compounds of hydrogen with nonmetals include ammonia (NH3), hydrogen sulfide (H2S), hydrogen chloride (or hydrochloric acid, HCl), hydrogen fluoride (or hydrofluoric acid, H2F2), and water (H2O).

The largest single use of hydrogen is in the production of ammonia. Ammonia, in turn, is used in the production of fertilizers and as a fertilizer itself. It is also a raw material for the production of explosives. Large amounts of hydrogen are also employed in hydrogenation, the process by which hydrogen is reacted with liquid oils to convert them to solid fats. Hydrogen is used in the production of other commercially important chemicals as well, most prominently, hydrogen chloride. Finally, hydrogen acts as a reducing agent in many industrial processes. A reducing agent is a substance that reacts with a metallic ore to convert the ore into a pure metal.

[See also Periodic table ]

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Hydrogen

Hydrogen


melting point: 259.14°C
boiling point: 252.87°C
density: 0.08988 g/L
most common ions: H+, H

Hydrogen was first recognized as a gaseous substance in 1766 by English chemist and physicist Henry Cavendish. The abundance of hydrogen in Earth's crust is 1,520 parts per million. The abundance of hydrogen in the universe by weight is 74 percent and by number of atoms is 90 percent. Hence, hydrogen is the major constituent of the universe. Under ordinary conditions (STP) on Earth, hydrogen is a colorless, odorless, tasteless gas that is only slightly soluble in water. It is the least dense gas known (0.08988 grams per liter at STP). Ordinary hydrogen gas (H2) exists as diatomic molecules. It reacts with oxygen to form its major compound on Earth, water (H2O). It also reacts with nitrogen, halogens , and sulfur, to form ammonia (NH3), hydrogen monohalide compounds (e.g., HCl) and hydrogen sulfide (H2S), respectively. It combines with several metals to form metal hydrides, and carbon to form a great many organic compounds.

Hydrogen is a mixture of three isotopes : protium (1H; atomic mass 1.007822); deuterium, or heavy hydrogen (2H or D; atomic mass 2.0140; 1 atom of 2H to every 6,700 atoms of 1H); and tritium (3H or T; atomic mass 3.016; has a radioactive nucleus). The fusion of protium nuclei (protons) to form helium is believed to be the major source of the Sun's energy. The extreme heat of reaction in hydrogen-oxygen burning is used in high temperature welding and melting processes. Hydrogen molecule addition reactions (hydrogenation) are widely used in industry, for example, for the hardening of animal fats or vegetable oils, for the synthesis of methanol from carbon monoxide, and in petroleum refining.

see also Cavendish, Henry; Explosions; Gases.

Ágúst Kvaran

Bibliography

Rigden, John S. (2002). Hydrogen: The Essential Element. Cambridge, MA: Harvard University Press.

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hydrogen

hydrogen (symbol H) Gaseous, nonmetallic element, first identified as a separate element in 1766 by English chemist and physicist Henry Cavendish. Colourless and odourless, hydrogen is the lightest and most abundant element in the universe (76% by mass), mostly found combined with oxygen in water. It is used to manufacture ammonia by the Haber process and in rocket fuels. Liquid hydrogen is used in cryogenics, including freezing human bodies with the hope of reviving them in the future. Properties: at.no. 1; r.a.m. 1.00797; r.d. 0.0899; m.p. −259.1°C (−434.4°F); b.p. −252.9°C (−423.2°F); most common isotope H1 (99.985%).

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hydrogen

hy·dro·gen / ˈhīdrəjən/ • n. a colorless, odorless, highly flammable gas, the chemical element of atomic number 1. (Symbol: H) DERIVATIVES: hy·drog·e·nous / hīˈdräjənəs/ adj.

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hydrogen

hydrogen (hy-drŏ-jĕn) n. a colourless gas that is combined with oxygen to form water (H2O) and with various other molecules (chiefly carbon and oxygen) to form all organic compounds. Symbol: H. h. ion concentration see pH.

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hydrogen

hydrogen XVIII. — F. hydrogène, f. Gr. húdōr, hudr- WATER; see -GEN.

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hydrogen

hydrogenabrasion, Australasian, equation, Eurasian, evasion, invasion, occasion, persuasion, pervasion, suasion, Vespasianadhesion, cohesion, Friesian, lesion •circumcision, collision, concision, decision, derision, division, elision, envision, excision, imprecision, incision, misprision, precisian, precision, provision, scission, vision •subdivision • television • Eurovision •LaserVision •corrosion, eclosion, erosion, explosion, implosion •allusion, collusion, conclusion, confusion, contusion, delusion, diffusion, effusion, exclusion, extrusion, fusion, illusion, inclusion, interfusion, intrusion, obtrusion, occlusion, preclusion, profusion, prolusion, protrusion, reclusion, seclusion, suffusion, transfusion •Monaghan • Belgian •Bajan, Cajun, contagion, TrajanGlaswegian, legion, Norwegian, region •irreligion, religion •Injun • Harijan • oxygen • antigen •sojourn • donjon • Georgian •theologian, Trojan •Rügen •bludgeon, curmudgeon, dudgeon, gudgeon, trudgen •dungeon • glycogen • halogen •collagen • Imogen • carcinogen •hallucinogen • androgen •oestrogen (US estrogen) •hydrogen • nitrogen •burgeon, sturgeon, surgeon

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Hydrogen

Hydrogen

Hydrogen is everywhere

The element

Discovery and preparation

Uses of hydrogen

Hydrogen disasters

Reactions of hydrogen

Hydrogen as a clean fuel

Resources

Hydrogen is the chemical element with atomic number 1. Its symbol is H, it has an atomic weight of 1.008, its specific gravity at standard temperature and pressure (1 bar, 0ºC) is 0.0000899. Its boiling point is 423.2ºF (252.9ºC), just above absolute zero. At room temperature, hydrogen is a colorless, odorless, tasteless gas that can combust, explosively or as a steady flame depending on conditions, in the presence of oxygen. It has two stable isotopes with mass numbers 1 and 2. A third isotope, tritium (mass number 3) is radioactive.

Hydrogen is first among the chemical elements. Its atoms are the simplest and lightest. A neutral hydrogen atom contains only one electron, and the most common isotope of hydrogen has a nucleus that consists of nothing but a proton. (A small percentage of hydrogen nuclei, deuterium or tritium nuclei, also contain one or two neutrons; this is discussed further below.) In the periodic table, it is in a class by itself; there are no other members of its exclusive group. It is usually placed at the top, all by itself.

Hydrogens name is a clue to its most important position among the worlds elements. It comes from the Greek hydro, meaning water, and genes, meaning born or formed. Hydrogen is thus the substance that gives birth to water. The name was coined in 1783 by the French chemist Antoine Lavoisier (1743-1794) in honor of the fact that when hydrogen burns in air it reacts with oxygen to form water, H2O.

Hydrogen is everywhere

There are roughly 170 million billion tons of hydrogen tied up in Earths supply of water. Hydrogen is therefore the most abundant of all elements on the surface of the Earth (though oxygen is the most abundant element in the crust, and the core is composed mostly of iron). Because the stars are mostly made of hydrogen, it is also the most abundant element in the universe, making up about 93% of all the atoms, and about three quarters of the mass of the entire universe. Most of the remaining one quarter of the universes mass is helium, with all other elements comparatively rare. Closer to home, 61% of all the atoms in the human body are hydrogen atoms.

Every one of the 13 million known organic compounds contains hydrogen. Hydrocarbonscompounds that contain nothing but hydrogen and carbon atomsare the foundation upon which the vast world of organic chemicals is built. The proteins, carbohydrates, fats and oils, acids and bases that make up all plants and animals are organic, hydrogen-containing compounds. Petroleum and coal, which are made from ancient plants and animals, are vast deposits of hydrocarbons.

Hydrogen is the source of most of the energy of the sun and stars. At the 10 million-degree temperatures of the interiors of stars, not only are hydrogen molecules separated into atoms, but each atom is ionizedseparated into an electron and a nucleus. The nuclei, which are simply protons, fuse together, forming nuclei of helium atoms and giving off a great deal of energy in the process. By a series of such reactions, all of the heavier elements have been built up from hydrogen in the stars.

The element

Hydrogen gas consists of diatomic (two-atom) molecules, with the formula H2. It is the lightest of all known substances. There is only about 0.05 part per million of hydrogen gas in the air. It rises to the top of the atmosphere and is lost into space. It is continually being replaced by volcanic gases, by the decay of organic matter, and from coal deposits, which still contain some of the hydrogen from when they were decaying organic matter.

There are three isotopes of hydrogen, two stable and one radioactive. Like all isotopes, they have the same number of protons in the nucleus (in this case, one) but differing numbers of neutrons. Hydrogen is the only element whose isotopes go by their own names: protium (used only occasionally, when it is necessary to distinguish it from the others), deuterium, and tritium. Their mass numbers are one, two, and three, respectively. Protium, the most common hydrogen isotope, constitutes 99.985% of all hydrogen atoms; it has no neutrons in its nuclei. Deuterium, the other stable isotope, has one neutron in its nucleus; it constitutes 0.015% of all hydrogen atomsthats about one out of every 6,700 atoms. Water made out of deuterium instead of protium is called heavy water; it is used as a moderatora slower of neutronsin nuclear reactors. Tritium has two neutrons and is radioactive, with a half-life of 12.33 years. In spite of its short lifetime, it remains present in the atmosphere in very tiny amounts because it is constantly being produced by cosmic rays. Tritium is also produced artificially in nuclear reactors. It is used as a radioactive tracer and as an ingredient of luminous paints and hydrogen bombs.

Discovery and preparation

Hydrogen is so easy to make by adding a metal to an acid that it was known as early as the late fifteenth century. Paracelsus (1493?1541) made it by adding iron to sulfuric acid, but it wasnt until 1766 that it was recognized as a distinct substance, different from all other gases, or what were then called airs. Henry Cavendish (17311810), an English chemist, gets the credit for this realization and hence for the discovery of hydrogen. Only in modern times, however, were isotopes of elements discovered. In 1932 Harold Urey (18931981) discovered deuterium by separating out the small amounts of it that are in ordinary water. This was the first separation of the isotopes of any element.

Hydrogen can be prepared in several ways. Many metals will release bubbles of hydrogen from strong acids such as sulfuric or hydrochloric acid. Hot steam (H2O) in contact with carbon in the form of coke reacts to produce a mixture of hydrogen and carbon monoxide gases. Both of these products are flammable, and this socalled water gas mixture is sometimes used as a fuel, although it is dangerous because carbon monoxide is poisonous. Passing an electric current through waterelectrolysiswill break it down into bubbles of oxygen gas at the anode (positive electrode) and hydrogen gas at the cathode (negative electrode).

Uses of hydrogen

Hydrogen and nitrogen gases can react to form ammonia:

N2
nitrogen gas
+3H2
hydrogen gas
2NH3
ammonia gas

This reaction, called the Haber process, is used to manufacture millions of tons of ammonia every year in the United States alone, mostly for use as fertilizer. The Haber process converts nitrogen from the air, which plants cannot use, into a form (ammonia) that they can use. In order to get the biggest yield of ammonia, the reaction has to be carried out at a high pressure (500 times normal atmospheric pressure) and a high temperature (842ºF [450ºC ]). To make it go faster, a catalyst is also used. More than two-thirds of all the hydrogen produced in the world goes into making ammonia.

A lot of hydrogen is used to make methyl alcoholabout 4 million tons of it a year in the U.S.:

2H2
hydrogen gas
+CO Carbon monoxide gasCH3OH
methyl alcohol gas

Methyl alcohol is a flammable, poisonous liquid that is used as a solvent and in the manufacture of paints, cements, inks, varnishes, paint strippers, and many other products. It is what burns in the camping fuel, Sterno.

Another major use of hydrogen is in the hydrogenation of unsaturated fats and oils. If the molecules of a fat contain some double bonds between adjacent carbon atoms, as most animal fats do, they are said to be unsaturated. Treating them with hydrogen gas fills up or saturates the double bonds: the hydrogen atoms add themselves to the molecules at the double bonds, converting them into single bonds. Saturated (allsinglebond) fats have higher melting points; theyre not as soft, theyre more stable, and they stand up to heat better in frying. Thats why hydrogenated vegetable oil on many food labels. Saturated fats raise peoples blood cholesterol and increase the risk of heart disease.

In the oxyhydrogen torch, the potentially violent reaction between hydrogen and oxygen is controlled by feeding the gases gradually to each other, thereby turning a potential explosion into a mere combustion. The resulting flame is extremely hot and is used in welding.

Hydrogen disasters

Liquid hydrogen, combined with liquid oxygen, is the fuel that sends space shuttles into orbit. The reaction between hydrogen and oxygen to form water gives off a large amount of energy. They are useful as a rocket fuel because in their liquid forms, large quantities of them can be stored in a small space. They are very dangerous to handle, however, because unless they are kept well below their boiling points (hundreds of degrees below zero), they will boil and change into gases. Under certain conditions, hydrogen gas in the air can explode, while oxygen gas can feed the slightest spark into a fiery inferno if there is anything combustible around. Mixed together, they make a highly explosive mixture. These sobering facts turned into disaster on January 28, 1986, when the Challenger space shuttle exploded shortly after liftoff, killing all seven astronauts aboard. A rubber seal had failed, spilling the explosive gases out into the jet of flame that resulted in the explosion of the center fuel tank.

An earlier flying tragedy caused by hydrogen was the explosion on May 6, 1937 of the German zeppelin (a dirigible, or blimp), Hindenburg. At that time, hydrogen was used as the lighter-than-air filling in dirigibles. The Hindenburg caught fire while mooring at Lakehurst, New Jersey after a transatlantic flight, and 36 people were killed. Ever since then, nonflammable helium gas has been used instead of hydrogen as the filling in dirigibles. It is not as buoyant, but it is completely safe.

Reactions of hydrogen

Having only one electron in each of its atoms, hydrogen has two options for combining chemically with another atom. For one thing it can pair up its single electron with an electron from a non-metal atom to make a shared-pair covalent bond. Examples of such compounds are H2O, H2S and NH3 (water, hydrogen sulfide and ammonia) and virtually all of the millions of organic compounds. Or, it can take on an extra electron to become the negative ion H-, called a hydride ion, and combine with a metallic positive ion. Examples are lithium hydride LiH and calcium hydride CaH2, but these compounds are unstable in water and decompose to form hydrogen gas.

Hydrogen reacts with all the halogens to form hydrogen halides, such as hydrogen chloride HCl and hydrogen fluoride HF. These compounds are acids when dissolved in water, and are used among other things to dissolve metals and, in the case of HF, to etch glass.

With sulfur, hydrogen forms hydrogen sulfide, H2S, a highly poisonous gas. Fortunately, hydrogen sulfide has such a strong and disagreeable odor that people can smell very tiny amounts of it in the air and take steps to put some distance between it and them.

Hydrogen as a clean fuel

When hydrogen burns in air, it produces nothing but water vapor. It is therefore the cleanest possible, totally nonpolluting fuel. This fact has led some people to propose an energy economy based entirely on hydrogen, in which hydrogen would replace gasoline, oil, natural gas, coal, and nuclear power. The idea is that hydrogen would be prepared by the electrolysis of sea-water in remote coastal areas and sent to the cities in pipelines similar to the pipeline that brings natural gas from Alaska to the lower states. In addition to being used as a fuel, the hydrogen could be used in factories to produce a variety of useful chemicals (see above). The main problem with this scheme is that the electricity to make the hydrogen would probably be made by burning coal, which (as burned today) is highly polluting, or by nuclear power, which is hardly uncontroversial. Renewable energy could be used to make hydrogen but this scheme is not yet affordable. In any energy-production scheme, the entire process must be considered, from beginning to end, with all of its ramifications. Only then can we decide whether or not there would be a net saving of energy or a reduction in overall pollution.

Resources

BOOKS

Lide, David R. Handbook of Chemistry and Physics. 87th ed. New York: CRC, 2006.

McWilliam, Andrew and Michael Rauch. Origin and Evolution of the Elements. Cambridge, UK: Cambridge University Press, 2004.

Sorenson, Brent. Hydrogen and Fuel Cells: Emerging Technologies and Applications. San Diego, CA: Academic Press, 2005.

Robert L. Wolke

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Hydrogen

Hydrogen

The lightest of all chemical elements, hydrogen has a density about one-fourteenth that of air. It has a number of special chemical and physical properties. For example, hydrogen has the second lowest boiling and freezing points of all elements. The combustion of hydrogen produces large quantities of heat, with water as the only waste product. From an environmental standpoint, this fact makes hydrogen a highly desirable fuel. Many scientists foresee the day when hydrogen will replace fossil fuels as our most important source of energy.

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Hydrogen

Hydrogen

Hydrogen is the chemical element of atomic number 1. Its symbol is H, it has an atomic weight of 1.008, its specific gravity at 32°F (0°C) is 0.0000899, and it melts at -434.7°F (-259.3°C). The boiling point of hydrogen is -423.2°F (-252.9°C), just above absolute zero . Boiling liquid hydrogen is the coldest substance known, with the exception of liquid helium. At room temperature , hydrogen is a colorless, odorless, tasteless gas. It consists of two stable isotopes of mass numbers 1 and 2.

Hydrogen is "number one" among the chemical elements. That is, it is the element whose atomic number is one. Its atoms are the simplest and lightest of all. A hydrogen atom contains only one electron , and it has a nucleus that consists of nothing but a proton . (A small percentage of hydrogen nuclei also contain one or two neutrons; see below.) In the periodic table , it is in a class by itself; there are no other members of its exclusive "group." It is usually placed at the top, all by itself.

Hydrogen's name is a clue to its most important position among the world's elements. It comes from the Greek hydro, meaning water , and genes, meaning born or formed. Hydrogen is a substance that gives birth to water (with a little help from oxygen ). The name was coined in 1783 by the French chemist Antoine Lavoisier (1743-1794) in honor of the fact that when hydrogen burns in air it reacts with oxygen to form water, H2O.


Hydrogen is everywhere

There are roughly 170 million billion tons of hydrogen tied up in the earth's supply of water. Hydrogen is therefore the most abundant of all elements on Earth . (Remember, there are twice as many hydrogen atoms in water as there are oxygen atoms.) Because the stars are mostly made of hydrogen, it is also the most abundant element in the universe, making up about 93% of all the atoms, and about three-quarters of the mass of the entire universe. Closer to home, 61% of all the atoms in the human body are hydrogen atoms.

Every one of the 13 million known organic compounds contains hydrogen. Hydrocarbons—compounds that contain nothing but hydrogen and carbon atoms—are the foundation upon which the vast world of organic chemicals is built. The proteins , carbohydrates, fats and oils, acids and bases that make up all plants and animals are organic, hydrogen-containing compounds. Petroleum and coal , which are made from ancient plants and animals, are vast deposits of hydrocarbons.

Hydrogen is the source of most of the energy of the sun and stars. At the 10-million-degree temperatures of the interiors of stars, not only are hydrogen molecules separated into atoms, but each atom is ionized—separated into an electron and a nucleus. The nuclei, which are simply protons, fuse together, forming nuclei of helium atoms and giving off a great deal of energy in the process. By a series of such reactions, all of the heavier elements have been built up from hydrogen in the stars.


The element

Hydrogen gas consists of diatomic (two-atom) molecules, with the formula H2. It is the lightest of all known substances. There is only about 0.05 part per million of hydrogen gas in the air. It rises to the top of the atmosphere and is lost into space . It is continually being replaced by volcanic gases, by the decay of organic matter , and from coal deposits, which still contain some of the hydrogen from when they were decaying organic matter.

There are three isotopes of hydrogen, two stable and one radioactive. Like all isotopes, they have the same number of protons in the nucleus (in this case, one) but differing numbers of neutrons. Hydrogen is the only element whose isotopes go by their own names: protium (used only occasionally, when it is necessary to distinguish it from the others), deuterium , and tritium . Their mass numbers are one, two, and three, respectively. Protium, the most common hydrogen isotope , constitutes 99.985% of all hydrogen atoms; it has no neutrons in its nuclei. Deuterium, the other stable isotope, has one neutron in its nucleus; it constitutes 0.015% of all hydrogen atoms—that's about one out of every 6,700 atoms. Water made out of deuterium instead of protium is called heavy water; it is used as a moderator—a slower of neutrons—in nuclear reactors. Tritium has two neutrons and is radioactive, with a half-life of 12.33 years. In spite of its short lifetime, it remains present in the atmosphere in very tiny amounts because it is constantly being produced by cosmic rays. Tritium is also produced artificially in nuclear reactors. It is used as a radioactive tracer and as an ingredient of luminous paints and hydrogen bombs.


Discovery and preparation

Hydrogen is so easy to make by adding a metal to an acid that it was known as early as the late fifteenth century. Paracelsus (1493?-1541) made it by adding iron to sulfuric acid , but it wasn't until 1766 that it was recognized as a distinct substance, different from all other gases, or what were then called "airs." Henry Cavendish (1731-1810), an English chemist, gets the credit for this realization and hence for the discovery of hydrogen. Only in modern times, however, were isotopes of elements discovered. In 1932 Harold Urey (1893-1981) discovered deuterium by separating out the small amounts of it that are in ordinary water. This was the first separation of the isotopes of any element.

Hydrogen can be prepared in several ways. Many metals will release bubbles of hydrogen from strong acids such as sulfuric or hydrochloric acid. Hot steam (H2O) in contact with carbon in the form of coke reacts to produce a mixture of hydrogen and carbon monoxide gases. Both of these products are flammable, and this so called" water gas" mixture is sometimes used as a fuel, although it is dangerous because carbon monoxide is poisonous. Passing an electric current through water—electrolysis—will break it down into bubbles of oxygen gas at the anode (positive electrode) and hydrogen gas at the cathode (negative electrode).

Uses of hydrogen

Hydrogen and nitrogen gases can react to form ammonia :

This reaction, called the Haber process, is used to manufacture millions of tons of ammonia every year in the United States alone, mostly for use as fertilizer. The Haber process converts nitrogen from the air, which plants cannot use, into a form (ammonia) that they can use. In order to get the biggest yield of ammonia, the reaction has to be carried out at a high pressure (500 times normal atmospheric pressure ) and a high temperature (842°F [450°C ]). To make it go faster, a catalyst is also used. More than two-thirds of all the hydrogen produced in the world goes into making ammonia.

A lot of hydrogen is used to make methyl alcohol—about 4 million tons of it a year in the U.S.:

Methyl alcohol is a flammable, poisonous liquid that is used as a solvent and in the manufacture of paints, cements, inks, varnishes, paint strippers, and many other products. It is what burns in the camping fuel, Sterno.

Another major use of hydrogen is in the hydrogenation of unsaturated fats and oils. If the molecules of a fat contain some double bonds between adjacent carbon atoms, as most animal fats do, they are said to be unsaturated. Treating them with hydrogen gas "fills up" or saturates the double bonds: the hydrogen atoms add themselves to the molecules at the double bonds, converting them into single bonds. Saturated (all-single-bond) fats have higher melting points; they're not as soft, they're more stable, and they stand up to heat better in frying. That's why "hydrogenated vegetable oil" on many food labels. Saturated fats raise people's blood cholesterol and increase the risk of heart disease .

In the oxyhydrogen torch, the potentially violent reaction between hydrogen and oxygen is controlled by feeding the gases gradually to each other, thereby turning a potential explosion into a mere combustion . The resulting flame is extremely hot and is used in welding .


Hydrogen disasters

Liquid hydrogen, combined with liquid oxygen, is the fuel that sends space shuttles into orbit . The reaction between hydrogen and oxygen to form water gives off a large amount of energy. They are useful as a rocket fuel because in their liquid forms, large quantities of them can be stored in a small space. They are very dangerous to handle, however, because unless they are kept well below their boiling points (hundreds of degrees below zero ), they will boil and change into gases. Under certain conditions, hydrogen gas in the air can explode, while oxygen gas can feed the slightest spark into a fiery inferno if there is anything combustible around. Mixed together, they make a highly explosive mixture. These sobering facts turned into disaster on January 28, 1986, when the Challenger space shuttle exploded shortly after liftoff, killing all seven astronauts aboard. A rubber seal had failed, spilling the explosive gases out into the jet of flame that resulted in the explosion of the center fuel tank.

An earlier flying tragedy caused by hydrogen was the explosion on May 6, 1937 of the German zeppelin (a dirigible, or blimp), Hindenburg. At that time, hydrogen was used as the lighter-than-air filling in dirigibles. The Hindenburg caught fire while mooring at Lakehurst, New Jersey after a transatlantic flight, and 36 people were killed. Ever since then, nonflammable helium gas has been used instead of hydrogen as the filling in dirigibles. It is not as buoyant, but it is completely safe.


Reactions of hydrogen

Having only one electron in each of its atoms, hydrogen has two options for combining chemically with another atom. For one thing it can pair up its single electron with an electron from a non-metal atom to make a shared-pair covalent bond. Examples of such compounds are H2O, H2S and NH3 (water, hydrogen sulfide and ammonia) and virtually all of the millions of organic compounds. Or, it can take on an extra electron to become the negative ion H-, called a hydride ion, and combine with a metallic positive ion. Examples are lithium hydride LiH and calcium hydride CaH2, but these compounds are unstable in water and decompose to form hydrogen gas.

Hydrogen reacts with all the halogens to form hydrogen halides, such as hydrogen chloride HCl and hydrogen fluoride HF. These compounds are acids when dissolved in water, and are used among other things to dissolve metals and, in the case of HF, to etch glass .

With sulfur , hydrogen forms hydrogen sulfide, H2S, a highly poisonous gas. Fortunately, hydrogen sulfide has such a strong and disagreeable odor that people can smell very tiny amounts of it in the air and take steps to put some distance between it and them.


Hydrogen as a clean fuel

When hydrogen burns in air, it produces nothing but water vapor. It is therefore the cleanest possible, totally nonpolluting fuel. This fact has led some people to propose an energy economy based entirely on hydrogen, in which hydrogen would replace gasoline, oil, natural gas , coal, and nuclear power . The idea is that hydrogen would be prepared by the electrolysis of sea water in remote coastal areas and sent to the cities in pipelines similar to the pipeline that brings natural gas from Alaska to the lower states. In addition to being used as a fuel, the hydrogen could be used in factories to produce a variety of useful chemicals (see above). The problems, however, are that hydrogen is a dangerous gas, and piping it around the country has its hazards. A more serious problem is that hydrogen is currently expensive, both in money and in energy cost. After all, where is the electricity supposed to come from in the first place, to electrolyze the sea water? It would have to be produced by burning coal or oil, which are hardly nonpolluting, or by nuclear power. In any energy-production scheme, the entire process must be considered, from beginning to end, with all of its ramifications. Only then can we decide whether or not there would be a net saving of energy or a reduction in overall pollution .


Resources

books

Brady, James E., and John R. Holum. Fundamentals of Chemistry. New York: Wiley, 1988.

Greenwood, N. N., and A. Earnshaw. Chemistry of the Elements. 2nd ed. Oxford: Butterworth-Heinneman Press, 1997.

Kirk-Othmer Encyclopedia of Chemical Technology. 4th ed. Suppl. New York: John Wiley & Sons, 1998.

Lide, David R., ed. Handbook of Chemistry and Physics. 73rd ed. CRC Press, 1992-3, page 4-14.

Parker, Sybil P., ed., McGraw Hill Encyclopedia of Chemistry. 1993.

Sherwood, Martin, and Christine Sutton, eds., The PhysicalWorld. New York, Oxford University Press, 1991.

Umland, Jean B. General Chemistry. St. Paul: West Publishing, 1993.

Robert L. Wolke

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Hydrogen

Hydrogen

INTRODUCTION: WHAT IS HYDROGEN ENERGY?

Hydrogen, the first element in the periodic table, is one of the most common elements found on Earth and the lightest one known to exist. An estimated 90 percent of the universe is composed of hydrogen. It can be found in nearly everything organic (that is, any material that contains the element carbon except diamond and graphite) and in all living organisms. In its pure gaseous form, hydrogen is odorless, colorless, tasteless, highly flammable, but not poisonous.

Many experts believe that hydrogen could be used as a fuel source to provide energy to the world. In order for this to happen, the gas must be in its pure form. This is problematic because hydrogen bonds (connects or attaches) relatively easily to other elements. In fact, it does not occur as a gas in nature but rather is found in combination with other elements. For example, hydrogen combines with oxygen to form water. Because water is so common, most methods to produce hydrogen gas focus on extracting it from water.

Electrolysis, a process that uses electricity, can separate the hydrogen from the oxygen in water. Photolysis detaches the elements from each other using sunlight instead of produced electricity. It is also possible to make the hydrogen industrially, by using methods such as steam reformation. In all cases, isolating the hydrogen yields a gas that is suitable for use as a fuel source.

Once the hydrogen is in pure form, it can be used several different ways. One use is to make a hydrogen fuel cell that can be used to power electrical generators or vehicles. Another is to use hydrogen to power an internal combustion engine (ICE), just like the ICEs that are already used to power cars and other vehicles. Using hydrogen in these ways can have both benefits and drawbacks, all of which are related to economical, societal, and environmental circumstances present in today's world.

HISTORICAL OVERVIEW

The use of hydrogen as a fuel source is not a modern notion. Scientists and visionaries have been experimenting with hydrogen since the seventeenth century. Its potential is still being explored in the twenty-first century.

Finding hydrogen

Hydrogen was first produced as early as 1671, when Robert Boyle (16271691), an English chemist, dissolved (mixed or melted) iron in acid. Boyle and other early scientists were unaware that hydrogen was a unique element. In fact, it was not until 1766 that hydrogen was officially recognized as an individual gas. Another English chemist, Henry Cavendish (17311810), measured the density of several gases to prove that hydrogen existed. He found that hydrogen was almost fourteen times lighter than ordinary air and called it "inflammable air" (meaning air that is likely to burn or explode).

Words to Know

Conductive
A material that can transmit electrical energy.
Electrolysis
A method of producing chemical energy by passing an electric current through a type of liquid.
Emission
The release of substances into the atmosphere. These substances can be gases, greenhouse gases, or particles.
Geothermal
Describing energy that is found in the hot spots under the Earth; describing energy that is made from heat.
Greenhouse gas
A gas, such as carbon dioxide or methane, that is added to the Earth's atmosphere by human actions. These gases trap heat and contribute to global warming.
Infrastructure
The underlying foundation or basic framework of a system, such as buildings or equipment.
Off-peak
Describing periods of time when energy is being delivered at well below the maximum amount of demand, often nights.

Following Cavendish's lead, a French scientist named Antoine-Laurent Lavoisier (17431794) repeated Cavendish's experiments in 1785 and gave hydrogen its name, from the Greek words hydro, meaning water, and genes, meaning forming. In addition, Lavoisier's process for isolating hydrogen (a rudimentary form of electrolysis) became the primary method for obtaining hydrogen gas up through the early nineteenth century.

Hydrogen balloon history

The history of hydrogen balloon flight began in France in December 1783, with the French physicist Jacques Charles (17461823). Charles and a companion, Noel Roberts, who helped build the balloon, were the first people ever to ascend in a hydrogen-filled balloon. They traveled 27 miles (43 kilometers) before the balloon came safely to rest. Charles is credited with the first solitary hydrogen balloon flight, during which he rose up 10,000 feet (3 kilometers) before landing again.

Hot Air or Hydrogen?

There is often confusion between the first hot air balloon flights and the first hydrogen balloon flights. Hot air balloon flights also originated in France but predated hydrogen flights by only a few months. Two Frenchmen, Joseph (17401810) and Étienne (17451799) Montgolfier, built a hot air balloon big enough to carry a basket, which in turn carried a duck, a sheep, and a rooster. This balloon's first flight occurred on September 19, 1783, only a few months before Jacques Charles's December flight that same year. The Montgolfier brothers went on to build several hot air balloons, one of which still holds a record as one of the largest balloons ever made. The balloon was flown by Joseph Montgolfier himself in 1784.

After the Montgolfiers' first flight, another Frenchman, Jean Blanchard (17531809), and John Jeffries, an American doctor from Boston, crossed the English Channel in a hot air balloon in 1785. Blanchard is also credited with the first hot air balloon flights in Germany, Poland, and the Netherlands. In 1793 Blanchard made a flight from Philadelphia, Pennsylvania, to New Jersey and delivered a letter, which became the first piece of airmail to travel in the United States. The ascent was witnessed by President George Washington, who with other onlookers, had paid Blanchard for the privilege.

The first hydrogen fuel cell

In 1839 Sir William Grove (18111896) built the first working fuel cell. Grove, an amateur scientist and a Welsh judge, was aware that an electric current (the movement or flow of electrons) could split a molecule of water into its component parts, hydrogen and oxygen, in a process known as electrolysis. He therefore deduced that, under the right circumstances, he might be able to produce water and electricity by combining hydrogen and oxygen. Grove conducted his experiment by putting strips of platinum into two different bottles, one full of hydrogen and one full of oxygen. He then placed the bottles into an electrolyte (a chemical substance that is capable of conducting current), in this case, sulfuric acid, where current began to flow and water accumulated in the gas bottles. Although Grove's fuel cell did work, he never found a practical use for it, and he never named it. Two chemists, Ludwig Mond and Charles Langer, coined the term fuel cell in 1889.

Moving on to airships

Airships were introduced in the nineteenth century and became another means of transportation that used hydrogen as a fuel source. Also known as a dirigible, an airship differs from a hydrogen balloon because it has a steering mechanism, often including an engine of some kind. There are three types of airships: a nonrigid airship, or a blimp; a semirigid airship, and a rigid airship (dirigible) or zeppelin, named after the first to build them, Count Ferdinand Adolf August Heinrich Zeppelin. All airships are sometimes known as LTA craft because the gas that provides their lift is lighter than air.

In the early twentieth century airships were used by the militaries of countries such as Germany and Great Britain. Airships also were sometimes used to carry passengers for long-distance travel. When airships were used as a means of transportation, they were often luxurious and expensive. Passengers sometimes boarded the airships to travel across the ocean. When traveling from Europe, for example, a person could reach the United States more quickly than by ocean liner.

One innovative airship that used hydrogen as the means of inflation was called the Akron. It was built in 1911 by Melvin Vaniman (18661912). The engine that powered the Akron could be run on gasoline or hydrogen. A flick of a lever changed which fuel was being used. Unfortunately, the Akron never got much use as a passenger carrier.

What's the Difference Between a Fuel Cell and a Battery?

A battery and a fuel cell are both electrochemical devices that convert chemical energy into electrical energy. The chemical reaction in a battery releases electrons that travel between the terminals and out as electricity. Moreover, when electricity is released from the battery, the battery's stored energy is being used up because the battery is a closed storage system. It can only produce so much energy before it dies and needs to be recharged or replaced. The fuel cell, on the other hand, is more of an energy converter than an energy storage device. Its chemical reaction converts hydrogen and oxygen into water and in the process produces electricity. A fuel cell will provide power as long as it is supplied with fuel. It does not run down or require recharging like a battery. A fuel cell can be refilled with hydrogen like filling an automobile gas tank.

Germany built the greatest number of hydrogen-filled airships. Some of these airships even traveled around the globe. One of the best known zeppelins was the Graf Zeppelin. It began running in 1928 and went around the world twice in 1929 alone. Over its ten-year active lifespan, the Graf Zeppelin traveled over one million miles (1,609,344 kilometers). It had no accidents, unlike many other hydrogen airships. In 1937 Hydrogen developed a negative reputation because of a disaster involving another German airship, the Hindenburg. International law now bans the use of hydrogen as an inflating gas for airships.

Syngas

Vehicles were not the only use of hydrogen in the late nineteenth and early twentieth centuries. Hydrogen is part of a fuel called syngas, which is also known as synthetic gas or town gas. Syngas is made up of as much as 50 percent hydrogen. It is made from coal, wood, and some waste that has been gasified (made into a gas). In the United States, syngas was first used as early as the late 1700s. It became a more common fuel in the late nineteenth century and until about 1940. Primarily used in urban areas to provide a fuel for heat and for cooking, it was also used in Europe and other parts of the world in the same time period. In Europe, syngas provided light for city streets, homes, and public buildings. It is still used in parts of China, Europe, and South America, where natural gas is not a fueling option.

Other twentieth-century research developments

Though some work on hydrogen as a fuel source was done in the nineteenth century, more work was done in the first half of the twentieth century. In the 1920s and 1930s European scientists and engineers experimented with the use of hydrogen as a fuel. Among their accomplishments was converting several types of vehicles to run on hydrogen, including trucks, a bus, and a railcar that was self-propelled.

In planes and space

Hydrogen did find some uses in aviation and the space program in this time period. Hydrogen was used to fuel a jet engine as early as the late 1950s on an experimental basis. By the late 1980s more research was being conducted in the United States and Russia in the use of plane engines fueled by hydrogen. Some supersonic jets might use hydrogen in the future, if the technology can be developed.

NASA has used hydrogen in various capacities since the 1950s. Hydrogen fuel cells provided power for the manned Gemini and Apollo space flights in the 1960s and 1970s. Fuel cells were used on these craft because they were seen as safer than nuclear power, another option that was considered. Another benefit of using hydrogen fuel cells on these flights was that the by-product of fuel cellswatercould be consumed by the astronauts. Liquid hydrogen has also been used in the space program as a rocket fuel to propel vehicles into space. In addition, space shuttles run by NASA since the 1980s have employed hydrogen as a fuel.

This use of hydrogen led to a tragedy. When a rubber seal failed on the space shuttle Challenger as it was lifting off in 1986, hydrogen gas mixed with the flame that was propelling the rocket Challenger into space. The mixture caused the space shuttle to explode. There were seven astronauts aboard, all of whom lost their lives.

First hydrogen research organization

There was continued interest in hydrogen as a fuel for other uses in the 1960s and 1970s. In the mid-1970s the modern era of hydrogen research began. In this phase, hydrogen was regarded as an energy source to replace fossil fuels. The first international conference was held in Miami Beach, Florida, and was called the Hydrogen Economy Miami Energy Conference. This event led to the founding of the International Association for Hydrogen Energy, an organization that in the 1990s helped get research off the ground and led to a growth of organizations, studies, and research all focused on hydrogen energy.

The Hindenburg Tragedy

In 1937, the German dirigible LZ 129, nicknamed the Hindenburg, traveled from Germany to the United States with a number of passengers. Including the crew, about 97 people were aboard. When the Hindenburg reached Lakehurst, New Jersey, the ship exploded, killing 36 people. Only 13 were passengers. The rest were crew members and one American who was on the ground at the time of the explosion. The investigation into the incident concluded that the hydrogen inside the dirigible probably caused the explosion. Investigators in the 1930s believed that electric discharge from the atmosphere ignited the hydrogen. Because of these findings, hydrogen began developing a negative reputation in the general public's mind.

This reputation was not deserved. Many years later, a scientist named Addison Bain (1935), who worked for NASA (the National Aeronautics and Space Administration) as manager of its hydrogen program, investigated the Hindenburg tragedy. He believed that the Hindenburg accident was not caused by the hydrogen exploding. He noted that the outer shell of the dirigible was a cotton cover that was painted with some flammable chemicals to both decorate and reinforce the airship's shell. Bain believed the substances were ignited by the static charges that had built up on the ship's metal frame as a result of a very stormy environment. What had been painted on the dirigible acted like rocket fuel. The resulting explosion caused the disaster.

Bain concluded that the flame color also revealed that the fire could not have been started by the hydrogen. Witnesses from 1937 reported that the flames were colorful. However, hydrogen burns almost clear

Twenty-first century developments

Several countries have put much effort into the study, support, and use of hydrogen as an alternative fuel for the future, including Canada, Japan, Germany, and the United States. Each country has its own vision, but most have pledged at least some public funding. The European Union has also pledged to spend money to help create hydrogen fuel cells through a partnership between in the daylight, the time when the incident took place. Despite Bain's findings, many people still believe that the hydrogen exploded and caused the disaster.

government and business. One country in particular, Iceland, has already committed to replacing its oil imports with hydrogen-fueled technology and is currently one of the largest consumers of hydrogen fuel.

Research in the United States

Most vehicles on the road today are powered by gasoline, which is produced from oil. Because oil will eventually run out, alternatives are needed to fuel vehicles in the future. A significant amount of money from both private and public sources is being invested in the early twenty-first century to develop hydrogen technology for vehicles in the United States. The concentrated movement to embrace hydrogen as an alternative energy began in 1990 with the passage of the federal Clean Air Act. This act called for a reduction in air pollution by changing the design of cars. The act also sought to change the kind of fuels that cars used so that their emissions (the waste by-product that is expelled by each vehicle) would be reduced. In addition, new emission standards were called for. Though hydrogen and other alternative fuels were not named specifically, hydrogen was a technology that was explored as a possible means of meeting this act's goal.

After the passage of the Clean Air Act, California was one state that pursued alternative energy technologies, including hydrogen. The state was especially interested in alternative fuels because the state had a major problem with air pollution. In California, which had about 30 million vehicles on the road as of 2005, about 90 percent of the population live where air quality cannot meet federal standards. California has addressed this problem in several ways. For example, some of the toughest standards for emissions in the United States can be found in California. Another way is through the work of the California Fuel Cell Partnership. This is a group dedicated to making fuel cells and vehicles that run on fuel cells part of American life. The partnership includes the government, companies that make fuel cells, energy providers, and car companies. In addition to educating the public about hydrogen fuel cell technology, the partnership works toward getting hydrogen fuel cell cars on the road and making hydrogen fuel stations available. By 2007 the partnership hopes to have 300 hydrogen fuel cell cars and buses on the road.

In 2002 and 2003 the United States made a significant commitment to embracing hydrogen in the form of fuel cell technology. In 2002, Secretary of Energy Spencer Abraham announced an initiative called FreedomCAR. A partnership between the federal government and U.S. car makers, this initiative pushed for research on hydrogen fuel cell technology. About $500 million was to be spent on this proposal.

President George W. Bush (1946) built on the proposal in his January 2003 State of the Union address. The president's proposal, called the FreedomCAR and Fuel Initiative, included spending $1.2 billion over five years in research conducted by both the government and private companies, such as car manufacturers, refineries, and chemical companies. The funds were designed to help create fuel cell technology for cars and trucks as well as homes and businesses. The hydrogen to power these cells would be created through electricity production, primarily from next-generation nuclear power plants and electric plants that run on coal. About $720 million of the funds were to go to building the infrastructure (the basic facilities, services and installations) needed to make the hydrogen, store it, and distribute it. Funds were included specifically to develop new technologies for cars, a significant issue in using hydrogen as a fuel source.

The federal government had a stated goal of putting hydrogen fuel cell cars on U.S. roads by 2010. The government hoped that hydrogen fuel cell cars would be the norm by 2020. The United States also supported the International Partnership for the Hydrogen Economy, which deals with the creation of the hydrogen economy on a worldwide basis. Some scientists and alternative energy supporters were critical of the proposal. Some were not pleased that other alternative energy sources did not receive money. Others were critical of the fact that the proposal still backed energy sources such as coal and nuclear power as the fuel to make the hydrogen. Coal, like oil, will one day run out, and many believe that hydrogen should be made from a renewable resource instead.

Japanese research

The Japanese government is very committed to developing hydrogen-based technologies because the country depends on foreign oil. The Japanese want to lessen or end their need for imported oil through the development of alternative energy sources such as hydrogen. The Japanese government spends several hundred million dollars each year on research into hydrogen fuel and fuel cells. In 2004 alone, the Japanese government spent $268 million on fuel cell research and development.

The Japanese government wants 50,000 cars powered by hydrogen fuel cells to be on the road by 2010. By 2020 the government wants the number to increase to five million. The government also hopes to have 4,000 hydrogen filling stations along Japanese roads by 2020.

Research in Canada and Germany

In the twentieth century Canada spent several decades researching fuel cellsnot using hydrogen, but an alkaline electrolyte or phosphoric acid as an electrolyte. Beginning in 1980 and into the late 1990s, the country started to experiment with hydrogen fuel cells. One company, Stuart Energy, promised to build five stations where vehicles could obtain hydrogen fuel by 2005. The Canadian government has pledged $500 million over five years, in the first decade of the twenty-first century, for fuel cell research.

In the 1950s Germany did research into alkaline fuel cells, while hydrogen research blossomed later in the century. By 2003 over 350 groups in Germany were working on hydrogen fuel cell technology.

Commitment in Iceland

Iceland wants to be the first country whose energy system is based on hydrogen. Iceland is a small island of only 40,000 square miles (64,374 square kilometers) near the Arctic Circle. The country's population is fewer than 300,000 people. Iceland's limited space and population make it an ideal place to test whether a hydrogen economy will work. The country decided to embrace hydrogen before the end of the twentieth century, with the goal of being fully hydrogen-based by midway through the twenty-first century.

Icelanders want to be self-sufficient in terms of energy. The country is already capable of producing more than enough of its own energy for heating and cooling purposes. However, because its population uses cars, buses, and ships, Iceland must import oil. This oil accounts for 30 percent of the country's energy consumption. Iceland wants to reduce this figure to zero. To reach this goal, a joint venture company was created in the late 1990s. It is called Icelandic New Energy and includes input from companies including Shell Hydrogen, Norsky Hydro, and DaimlerChrysler. In 2000 the company began creating the infrastructure for production and distribution of hydrogen as fuel. Iceland has already decided that most of its hydrogen energy will come from fuel cells, which will be used in generators and vehicles.

By 2003 Iceland had its first hydrogen retail outlet, a Shell filling station, in its main city of Reykjavik. Hydrogen was produced on site using hydroelectric and geothermal energy to power the reaction. The hydrogen produced there was also being stored and distributed to other locations. Some of the first users of this hydrogen filling station were three public transit buses. These buses look like standard buses, but they are taller because the hydrogen tanks are located on the roof. Iceland has faced some problems with these buses. They must be kept inside at night so they keep warm. Officials do not want to have the water emitted by the fuel cells freeze and damage the cells. While the buses are being gradually introduced, Iceland next wants to get automobiles that run on hydrogen fuel cells to be the standard vehicle of choice. The country expects to introduce such cars in 2006.

Down the road, a bigger challenge will be getting boats and ships to run on hydrogen technology. Most of Iceland's fossil fuel consumption comes from the use of boats for fishing, a staple of the Icelandic economy. Powering boats with fuel cells is more challenging because a trawler (a boat designed to catch fish by dragging large nets), for example, carries a large amount of gasoline and stays at sea for several days. More hydrogen than that would be needed for a trip of the same length. The Icelandic government will have to convince those who use boats to accept hydrogen as a fuel. Iceland wants to run exclusively on hydrogen by 2050.

PRODUCING HYDROGEN

Hydrogen is sometimes considered to be the energy source of the future, for a few reasons. One reason for this belief is that hydrogen is renewable. Unlike the fossil fuels upon which the world is currently dependent, hydrogen can be produced or "created" and in a short amount of time. There are several methods by which hydrogen can be produced, including, but not limited to, electrolysis and steam reforming.

Electrolysis

Electrolysis is the process by which an electric current is passed through water and breaks the chemical bonds between hydrogen and oxygen. An electrolyte, a fluid chemical substance that can carry a current, aids in the bond-breaking procedure. Once the bonds are broken, the atomic components (hydrogen and oxygen) become either positive or negative ions (charged particles). Two terminals (anode and cathode) also have positive and negative charges, drawing the resulting ions toward them. Generally, the positive hydrogen ions gather at the anode (which is negative), while the negative oxygen ions reside at the cathode (which is positive). Gas is then formed at either terminal.

It is possible to perform electrolysis at high temperatures. High temperature electrolysis (HTE), also known as steam electrolysis, operates much the same way as conventional electrolysis. The variation occurs in that, rather than using a standard amount of electric current, heat is applied instead. This reduces the total amount of electric energy required to produce hydrogen gas.

Steam reforming

Steam reforming, sometimes called reforming or steam methane reforming, is another well-known method for making hydrogen. Natural gas is the most common fuel used in steam reforming. To make hydrogen using steam reforming, natural gas is reacted with steam at a very high temperature in a combustion chamber. The temperature can be from 1472°-3982°F (800°-1700°C).

A catalyst (a substance that increases the rate of a reaction without being consumed in the process) is present in some steam reformers. The catalyst is usually made of metal. The catalyst helps break up the natural gas into methane. When the methane and water react, hydrogen is produced. Carbon oxides such as carbon monoxide and carbon dioxide are made as by-products. In some processes, the carbon monoxide is reacted again to form more hydrogen and carbon dioxide.

The steam reforming process has some positive points. Of all the fossil fuels, natural gas is the cleanest burning. In other words, it gives off fewer by-products that can contribute to pollution. The use of natural gas to make hydrogen might help in the creation of an infrastructure for the distribution of hydrogen. Since there are stations that already distribute natural gas, the natural gas could be transported there and converted to hydrogen via steam reforming on site and on a small scale. This means of production could provide hydrogen for cars that run on either hydrogen fuel cells or hydrogen-powered internal combustion engines.

Benefits and drawbacks of existing production methods

Each hydrogen-producing method has its own benefits and drawbacks. Electrolysis is considered to be the most environmentally friendly procedure, because it produces no by-products that are harmful to the environment. In addition, it has a potentially positive by-product: oxygen. This oxygen could be captured and used elsewhere.

However, large-scale production of hydrogen by electrolysis becomes very expensive because electricity is used to create the electric currents. If renewable energy sources such as solar energy, hydropower, hydroelectric power, or even nuclear power were used to produce the current, the process would become much more affordable. Another source of energy could be obtained through the use of biomass: waste, sewage, and agricultural residue are all endlessly renewable and have little negative effect on the environment.

Other Production Methods

Scientists from around the world are trying to find the best way to make hydrogen from renewable resources and have come up with many unique ideas. For example, since the 1940s, scientists have worked to use algae (such as pond scum) to make hydrogen. Algae naturally produce hydrogen from water using sunlight energy, a process called photolysis. More recently, a scientist in England, Murat Dogru, proposed that hazelnuts could provide a source of hydrogen, because hazelnut shells produce hydrogen when they are burned.

Bacteria are also being investigated as a way to make hydrogen, but this is not commercially practical yet. Bacteria react like algae in water and can naturally separate the hydrogen and oxygen using sunlight. Experiments are being conducted to alter the structure of the bacteria so that they produce less oxygen and more hydrogen to be used as fuel. Another method of producing hydrogen employs microbes (microorganisms). These microbes are used to make biomass (the leftovers from crops that cannot be used anywhere else) into hydrogen.

Another potential innovation begins with biogas (containing methane, carbon dioxide, water vapor, and other gases) that is caught from the gaseous releases of dairy cows. The biogas is converted to hydrogen and used to power fuel cells. The fuel cells are intended for use in hydrogen-powered generators on the farms. In 2004 scientists working at the University of Minnesota, Twin Cities, discovered a way of taking corn, fermenting it, producing ethanol, and converting it into hydrogen fuel.

The steam reforming process is the most common method used to make hydrogen industrially. One benefit is that it is cheaper than producing hydrogen by electrolysis. However, a big drawback is the amount of carbon dioxide produced during the process. If the steam reforming process is to catch on as a means of mass-producing hydrogen fuel, the issue of what to do with the carbon dioxide produced must be addressed. Carbon dioxide can build up and trap heat on the planet. This condition is known as global warming. Potential solutions to the carbon dioxide issue with steam reforming exist, and all are costly. The carbon dioxide could be stored in empty gas wells or oil wells where the reservoirs of gas or oil have been depleted. Saline aquifers, which are underground pockets of saltwater, are another storage possibility. So are coal seams (where coal can be found) that are so deep underground that they cannot be mined.

While the amount of space available to store the carbon dioxide is limited, there is enough space to be able to store the gas produced for many years. However, there is some danger to storing the carbon dioxide. If it mixes with a freshwater aquifer (underground stream) or gets to the surface, it could change the chemistry of the soil. Even worse, if the carbon dioxide should leave its storage space and end up in a place that is a depression without wind, the gas, which is heavier than air, could start to collect. If enough carbon dioxide collects, it could suffocate animals or people. This tragedy has happened in the past. In 1986 in Cameroon, 1,800 people died after 87 million cubic yards (80 million cubic meters) of carbon dioxide erupted from a volcanic crater.

Another potential problem with steam reforming is that the natural gas needed for the process is available in only a limited supply, like all fossil fuels. Steam reforming produces hydrogen on a large scale, but a method needs to be developed to do steam reforming on a smaller scale so this reaction can take place either on the vehicle or at a filling station that supplies hydrogen.

USING HYDROGEN

The most commonly researched and most developed application of using hydrogen as a fuel source is in conjunction with a hydrogen fuel cell. Fuel cells operate by mixing hydrogen and oxygen to produce water and electricity. The electricity can then be used to provide power to homes, schools, and even businesses or to power cars and other vehicles. Some experts believe that internal combustion engines (ICEs) that are fueled by hydrogen are just as important. Hydrogen could be used as fuel for transportation by creating internal combustion engines for vehicles that run on hydrogen or hydrogen fuel mixtures.

Using hydrogen in fuel cells

A fuel cell works sort of like a battery. In hydrogen fuel cells, the hydrogen is converted to electricity through an electrochemical reaction. A fuel cell does not run out of power as long as its fuel, hydrogen, is present. There are several types of fuel cells. Some use phosphoric acid as an electrolyte (a substance that conducts electricity). Others use molten carbonate as electrolytes.

The most common type of hydrogen fuel cell in use is the proton exchange membrane (PEM) fuel cell. General Electric first invented this fuel cell in the 1960s as a source of electrical power for the Gemini spacecraft. Though they were expensive, these fuel cells were efficient producers of energy.

PEM fuel cells are usually stacked when they are used in vehicles. That means a number of identical fuel cells are put together to provide a significant amount of energy. The more fuel cells that are put together, the more voltage created. The number of fuel cells stacked in each vehicle varies by the amount of power needed.

Hydrogen fuel cell vehicles

While fuel cells were used early in the United States space program, most discussion of hydrogen fuel cells has focused on vehicles such as cars, buses, and vans. Most major car companies around the world are working on fuel cell technology in some form. Each company has produced its own concept cars and is working toward solving the problems related to building such cars on a mass scale. Even a high-end, limited production company like Rolls Royce has researched hydrogen fuel cells for cars. This company is hoping to have a fuel cellpowered hydrogen prototype completed by 2008. Rolls Royce has been working on hydrogen fuel cell research since 1992.

Daimler Chrysler began research on fuel cells in the 1990s. The company's first fuel cell car was introduced in 1994 and called NECAR 1. Many different versions followed, some of which were tested on the road. In 1997 the car company also introduced a fuel cell bus called the NEBUS. This was followed later with the Mercedes-Benz Citaro bus. About thirty of these buses were used on a test basis in cities throughout Europe between 2003 and 2006.

General Motors (GM) has been working on hydrogen fuel cell technology for many years. The company produced its first fuel cellpowered car in 1966. Though this research area was dropped soon after, GM resumed its work on hydrogen fuel cells in the early 1980s. By the early 2000s GM had about six hundred employees researching fuel cells. The company formed a partnership with Toyota in 1999 to share hydrogen fuel cell research.

Some of GM's experimental vehicles have been used on a limited basis. In 2003 Federal Express agreed to use one of GM's fuel cell vehicles for one year on normal routes to see how it would work. GM has also conducted test runs of one of its hydrogen fuel cell cars, the HydroGen 3. This vehicle contains 200 hydrogen fuel cells and costs about $1 million to build. HydroGen3sare being used by the federal government in Washington, D.C., on an experimental basis.

Toyota and Honda also have invested in hydrogen fuel cell technologies. Beginning in 1992 Toyota started working on fuel cell hybrid vehicles, coming up with four prototypes. Road testing of one of the company's fuel cellpowered cars began in 2002. These cars were used at the University of California, Irvine, and University of California, Davis.

Honda began its research into this technology in 1989. Its fuel cell vehicles have been tested on roads in the United States since about 1999. One concept car, the Honda FCX, was tested by the city of Los Angeles in 2002. In 2003 this vehicle was certified for commercial use by the Environmental Protection Agency and the California Air Resources Board.

A number of countries are using hydrogen fuel cellpowered buses on an experimental basis. From 1998 to 2000 several hydrogen-powered buses were used in Chicago and in Vancouver, British Columbia, Canada. British Columbia later bought three other buses to use experimentally in the early 2000s. Vancouver had more buses delivered in 2005 for a further three-year experimental run. In London, England, three of these buses began running in 2003.

Fuel cells as generators

Though most of the media attention has focused on hydrogen fuel cells in vehicles, hydrogen fuel cellpowered generators are already being used in at least 600 buildings around the world. Hospitals, data centers, and office buildings use this technology in their backup generators. Some businesses use these fuel cell generators as part of their source of power. For example, fuel cells provided about 15 percent of the power at a major office building, 4 Times Square, in New York City in 2003.

Using hydrogen in ICEs

When discussing hydrogen as a fuel source, most of the focus in the twentieth and early twenty-first centuries has been on fuel cells. However, some experts believe that internal combustion engines (ICEs) that are fueled by hydrogen are just as important. One early believer in this vision was German researcher Rudolf Erren. He was concerned with the amount of oil his country imported and the emissions that automobiles produced well before most countries took note of these issues. In 1930 he saw that hydrogen could be used as fuel for transportation. He believed that this hydrogen should be produced by water electrolysis. Erren spent time working on creating internal combustion engines for vehicles that could run on hydrogen or fuel mixtures that included hydrogen.

Hydrogen-powered ICEs are intended for use in buses, cars, vans, and other types of vehicles. Although car manufacturers have already created some hydrogen ICEs, there has not been as much focus on the development of hydrogen ICEs as on hydrogen fuel cells. BMW is one manufacturer that has focused primarily on developing a hydrogen ICE. The company began this research in 1978. Since then BMW has developed several kinds of hydrogen ICEs, which use various hydrogen-to-air ratios, depending on the power desired. The company has also explored using liquid hydrogen as opposed to hydrogen's gaseous form. When liquid hydrogen is used, the car does not need to be refueled as often.

How an Internal Combustion Engine Works

An internal combustion engine (ICE) is a vehicle engine in which the combustion of the fuel takes place within internal cylinders. Virtually all cars today use internal combustion engines, with gasoline as the fuel. A hydrogen ICE is not unlike a gasoline-powered ICE. The hydrogen provides power to create the explosions in the engine that power the car. Inside the engine, pistons move up and down within their cylinders. As each piston pushes up, it compresses a mixture of fuel (hydrogen or gasoline) and air. As the piston reaches the top, the combination of fuel and air is ignited by a spark plug. This explosion forces the piston down inside the cylinder. The ignited fuel also turns the crankshaft in the engine, which eventually leads to the wheels of the car turning. The piston again pushes up in the cylinder to make the exhaust from the ignition move out of the valves located at the cylinder's top. After this step, the piston returns to the bottom of its cylinder. This movement allows another mix of air and fuel to fill the cylinder. This mixture comes in through another set of valves. Then the process begins again.

Interestingly, most of BMW's hydrogen ICEs can run on gasoline as well as hydrogen. One BMW concept car that can run on either hydrogen or gasoline is called the H2R. This car was introduced in 2005. The engine in this vehicle is very similar to a standard gasoline ICE that BMW uses in another car, the 760i. Though the engine in the H2R can run on hydrogen, it has an efficiency level similar to a traditional engine. Because the engine in the H2R can run on gasoline or hydrogen, the driver has flexibility in fueling. This quality can be especially important if the hydrogen runs out. A tank of hydrogen only lasts about 215 miles on the H2R, much less than a similar tank full of gas. BMW hopes to sell cars using this type of ICE in Europe by 2007 or 2008. The company wants to put them on the market in the United States by about 2010.

Another car company, Ford, has divided its research focus between hydrogen ICEs and fuel cell cars. The company has developed several hydrogen ICE concept cars, including one car called the Model U and a version of the Ford Focus. Ford also has worked on other vehicles that use hydrogen ICEs, including vans and buses. Ford hopes to have 100 such vans in service by 2006. As for its buses, they were first tested at the 2005 Detroit Auto Show, where they were used as shuttles for reporters. In 2006 the company will sell some of these buses to the state of Florida.

Benefits and drawbacks of existing hydrogen technologies

Each use of hydrogen as fuel has specific benefits and drawbacks. Hydrogen fuel cells are already in use as electrical generators, and they have also been used in the space program. Most experts believe the fuel cell is likely to be the dominant hydrogen technology in the future, not only for electrical generation but also to power vehicles. The only by-product of using a hydrogen fuel cell to power a car is water or water vapor, which exits through the tailpipe. However, hydrogen ICEs are so similar to existing gasoline ICEs that they could be the best first use of hydrogen as a transportation technology for the general public. Also, like fuel cells, hydrogen ICEs do not produce harmful by-products.

Benefits and drawbacks of hydrogen fuel cells

Hydrogen fuel cells have many good aspects. Fuel cells are very easy to make. They contain no moving parts. This means that there is little maintenance that needs to be performed on each fuel cell. Because they have no moving parts, fuel cells are quiet. Fuel cells are also light and versatile. They can be manufactured big or small and used on a large or small scale. Because they are modular in design, one can work on its own or many can function together as one.

Hydrogen fuel cell-powered cars are very efficient producers of power. They are more efficient than internal combustion engine cars. About 60 percent of the potential energy in hydrogen is made into electricity by a fuel cell. These fuel cell-cars can respond instantaneously to provide fuel when it is needed.

Yet there are several major drawbacks to the development and use of fuel cells. One is the lack of a worldwide standard for fuel cells between manufacturers or most governments. Only one standardization agreement was in place as of 2005. It was between Japan and the European Union. This agreement covered hydrogen fuel cells for automobiles. Because no standards are yet in place, the development of the infrastructure needed to support hydrogen technology has been delayed. Governments and businesses do not want to invest money in creating an infrastructure that could be useless if it does not match the standards that others use.

The cost of the energy produced by a fuel cell is also very high. It costs more per kilowatt produced when compared to a gasoline-powered combustion engine. In 2002 a fuel cell could cost anywhere from $500 to $2,500 per kilowatt produced, while the combustion engine only cost about $30 to $35 for the same amount of energy. The costs for fuel cells have been going down as technology has been developed and improved.

Benefits and drawbacks of hydrogen-powered ICEs

One positive aspect to hydrogen-powered ICEs is that engineers at car companies are already experienced in the construction of such engines. The engines are similar to gasoline-powered ICEs. These types of ICEs are more familiar to automotive engineers than the technology of fuel cell engines. These vehicles will also be simpler internally than gasoline-powered cars. The catalytic converters and related systems found on gasoline-powered ICEs to clean up the by-products of fossil fuel combustion are not needed if hydrogen is used.

But hydrogen-powered ICEs have several disadvantages. The cars that use this type of engine are not as efficient as fuel cell-powered cars. Hydrogen ICEs can only extract about half of the chemical energy that is contained in a unit of hydrogen as compared to a fuel cell-powered vehicle. The vehicles also need more space to store fuel than gasoline-powered ICEs. These vehicles are built on current fuel tank sizes designed for gasoline or diesel fuel. Because hydrogen is not a very dense gas, the tanks cannot hold very much hydrogen. Therefore, the vehicles cannot travel as far.

TRANSPORTING HYDROGEN

The form of hydrogen transportation depends on the form of hydrogen being transported. There are different methods for transporting gaseous hydrogen and liquid hydrogen. Most of these methods are still being developed and refined; they are not yet in large-scale use.

Transporting gaseous hydrogen

In its gaseous form, hydrogen could be transported over a network of pipelines. Pipelines are commonly used today to distribute hydrogen over a short distance for industrial use, but a wider system would have to be introduced if hydrogen becomes the fuel source of choice for vehicles, homes, and businesses. This pipeline system could be similar to the way that natural gas is distributed. The hydrogen pipeline system also would need more compressors than a natural gas system. A small amount of hydrogen that is traveling along the pipeline would have to be used to power the compressors. Some experts believe that one way to address the distribution question is by converting natural gas pipeline systems to hydrogen. These supporters believe that only the seals, the meters, and the equipment at the end of the pipeline would have to be modified to support hydrogen. There are also trucks that transport hydrogen as a compressed gas, but they hold a much smaller quantity than a gasoline tanker.

Transporting liquid hydrogen

Transporting the liquid form of hydrogen could take many forms. As gasoline is now, hydrogen could be transported via truck, railcar, or ship. This method could be expensive and difficult. It would take about 21 tanker trucks of hydrogen to carry the equivalent of one gasoline tanker because hydrogen has a low density.

Benefits and drawbacks of hydrogen transport methods

The infrastructure to transport hydrogen does not yet exist. Some experts believe that the questions about how to produce, distribute, and store the hydrogen have to be answered all at once for the infrastructure to be properly implemented. Regardless of which methods are eventually used, it will still cost billions of dollars to create this transportation infrastructure. That cost is one large obstacle to the development of better transportation methods.

DISTRIBUTING HYDROGEN

At least in the case of hydrogen-powered vehicles, the primary means by which hydrogen would be distributed for public consumption is through a hydrogen filling station. Such a station would be like a gas station, only with hydrogen instead of gasoline. As of 2005 there were only about 100 hydrogen filling stations in existence in the world.

By 2005 the Clean Urban Transport for Europe program was expected to build several hydrogen filling stations in major European cities. Germany is especially committed to building hydrogen filling stations. The German government is helping to pay for the building of the self-sufficient hydrogen filling stations as a step toward the hydrogen economy.

The United States government has also made a commitment to building hydrogen filling stations. In 2004 the U.S. Department of Energy promised to spend $190 million to build gas stations that would offer both hydrogen and gasoline. The money is also intended to support other projects related to the development of the infrastructure needed to support the hydrogen economy. This money will be spent, however, only if private industry will match the amount.

A few hydrogen filling stations already exist in the United States. In 2005 in Washington, D.C., the first hydrogen-gasoline fueling station was opened by Shell. It provides hydrogen for the six fuel-cell cars that General Motors provided to the area. Both the cars and the station were demonstrations to show the potential of hydrogen as a fuel source. The state of California is also committed to building hydrogen filling stations. By 2010 the California government has promised to have 150 to 200 hydrogen fueling stations on the interstate highways in California as part of the California Hydrogen Highway Network. They will be located on all 21 of the state's interstate freeways. Under the California plan, hydrogen filling stations will be found every 20 miles to provide convenient access for consumers.

Benefits and drawbacks of hydrogen distribution methods

One large benefit to using filling stations to distribute hydrogen fuel is that consumers all over the world already use such stations to fill their gasoline-powered cars. The general public would not need to be educated on the concept of using filling stations for their automobiles.

However, there are drawbacks with this technology. In Europe, for example, the electrolysis system is often employed to convert water to hydrogen at the filling stations. The problem with this kind of filling station is the large amount of electricity needed to make the conversion possible. Electricity is expensive, and current electricity generation depends heavily on fossil fuels. In Germany, experiments are being conducted to use wind as a source of electricity for on-site electrolysis at filling stations. In the United States, wind-driven on-site electrolysis at filling stations is not seen as feasible in most parts of the country. Instead, biomass is the method being examined. In this process, waste from logging and lumber as well as leftover crop plants is used to produce the electricity needed.

In addition to working on the technology behind hydrogen filling stations, governments and companies have to build the stations. The cost will be enormous, and many governments have pledged funds for this to happen.

STORING HYDROGEN

Hydrogen is usually stored as a liquid, though it can also be stored as a gas or a solid. Because hydrogen is low in density, storing it is a challenge. This is true both for storage at hydrogen production sites as well as on vehicles that might use hydrogen as a fuel. Among the methods for storing hydrogen are the following:

  • Compressing it into cylinders of various sizes. This is one of the most common ways to store hydrogen for industrial use.
  • Using compressed gas tanks for vehicles. Many automotive manufacturers and researchers have been experimenting with these tanks. Instead of cylinders, hydrogen would be pumped into a compressed gas tank on the car and stored there.
  • Storing liquid hydrogen cryogenically (at very low temperatures).

Benefits and drawbacks of storage options

Storage of hydrogen on vehicles is a major concern. Some scientists believe that the storage of hydrogen on cars is the biggest single problem facing the use of hydrogen as a fuel for cars. Vehicles have very limited space for storing hydrogen, and the amount that needs to be stored for hydrogen to be a viable fuel source is rather large.

As mentioned, hydrogen is usually stored as a liquid. However, liquid hydrogen has many drawbacks. For example, liquid hydrogen has to be stored at temperatures at or below 423°F (253°C). To keep the liquid this cold requires a significant amount of energy. The system also must be insulated. Also, even if liquid hydrogen is stored at the right temperature, about three to four percent is boiled off daily. This situation could be a problem for vehicles that are not being used for a few days at a time.

Because of the low density of hydrogen, the amount of hydrogen that can be compressed into a cylinder is less than more dense substances. This problem means that compression has a significant energy cost and an economic expense. The cylinders also must be transported from the place the hydrogen is manufactured to the market where it is needed.

The same drawback hinders compressed gas tanks on vehicles. As of 2005 most compressed gas tank systems can only carry about 5,000 pounds per square inch (psi) of hydrogen. For the ideal range for a car, researchers hope to develop a tank system that offers 10,000 psi. For now compressed gas tanks are large and hard to fit onto a car. They are also made from materials that are both heavy and expensive. One such material is carbon fiber. There are also safety concerns for hydrogen compressed gas tanks. To be safe, they must be able to withstand a very powerful impact. This is a goal that has not been fully reached in a workable manner.

IMPACTS

Using hydrogen as an alternative energy source would have numerous impacts. Perhaps the biggest would be in the environmental arena, as the development of hydrogen-powered vehicles could drastically reduce the pollution that contributes to global warming, depending on the production method. In addition, because the fossil fuels that currently are used for most of the world's power will one day run out, society will need to find alternative energy sources to power its homes, businesses, and transportation needs. Hydrogen can be an important part of this alternative future. However, not all of the potential impacts are positive ones.

Environmental impact

Much of the impact of adopting hydrogen as an energy source would be positive for the environment. The use of hydrogen would likely come with a reduction of the use of fossil fuels as energy sources. With this reduction would perhaps come a reduction in global warming, because fossil fuel use is believed to be an important contributor to global warming.

However, the production of hydrogen can potentially affect the environment in a negative way. Depending on the production method, carbon dioxide and other negative emissions can enter the atmosphere while hydrogen is being made. This issue can be addressed by catching and storing the carbon dioxide, but even this storage can potentially affect the environment. However, if environmentally friendly, renewable resources such as solar or wind are used to power the means of producing hydrogen, the negative impact can be eliminated.

Another potential problem is that if hydrogen becomes widely used, it could leak into the atmosphere. If the amount is significant enough, this hydrogen could change the percentage of hydrogen present in Earth's atmosphere. Some scientists believe that this could have a profound effect on the atmosphere, including increasing the size of the hole in the ozone layer. More hydrogen in the atmosphere could also lead to more high altitude clouds and increase the number of soil microbes that rely on hydrogen as their primary nutrient. The soil microbe increase could change the ecology of Earth. However, there are soil micro-organisms that consume hydrogen as well, and they might be able to balance these problems out. The outcome of putting more hydrogen in the atmosphere is uncertain.

A final environmental question is what to do with the water or water vapor that would be produced by cars using hydrogen fuel cells. Since such water is pure, it will freeze in temperatures below 32°F (0°C). Scientists will have to come up with a solution for this by-product on the roadways and the environment in colder climates.

Economic impact

Adopting a hydrogen-based economy could lead to an extreme change in a number of industries. The way the automotive business would be run would change completely as these companies focused on building cars, trucks, and buses that use hydrogen instead of gasoline. The oil/petroleum business would suffer at some point as the use of hydrogen creates less dependence on oil. The adoption of hydrogen could also impact the electric industry, especially if electrolysis is widely adopted as a means of producing hydrogen.

Whole new industries would also be created as the infrastructure needed to support hydrogen is put in place. The production, transportation, distribution, and storage of hydrogen could have a huge economic impact as billions of dollars would be invested around the world to create the infrastructure for the hydrogen economy. As this infrastructure is put in place, those who could fix and maintain hydrogen filling stations, production plants, generators, vehicles, and other such hardware would be needed. This would create new jobs and businesses.

Automotive manufacturers in 2005 expect hydrogen-powered ICE cars to hit the marketplace within five to ten years. Because the public might embrace hydrogen-powered ICEs more easily than fuel cell-powered cars, some observers believe that if these kinds of vehicles can get on the market, the hydrogen economy can grow rapidly. The spread of cars with hydrogen ICEs would create a demand for hydrogen fuel and a place to buy it.

The development of hydrogen fuel cells would also have an economic impact. In addition to creating an industry for the production of fuel cells themselves, the manufacturing processes used for vehicles, generators, and other products that use fuel cells would change.

Societal impact

The implementation of the hydrogen economy would affect society worldwide. In countries that are already developed, such as the United States and Great Britain, sources of power and the way vehicles run and even sound would be different. Fueling cars would also be a somewhat different experience than it is right now.

Hydrogen could also change the way the whole power grid works. Currently, developed countries receive their power from centralized power stations. These stations produce the electrical power from fossil fuels of one kind or another and then send the power through wires to individual businesses and homes. If a power station goes out, all the homes and businesses connected to it on the grid also go out. In a hydrogen-based system, individual fuel cell sites could generate electricity for homes and businesses independently. If the overall power grid were to become less centralized, it would be less vulnerable to terrorist attacks aimed at crippling a nation's energy supply.

Even hydrogen fuel cellpowered vehicles might act as small generators and provide power for others when they are not in use. The cars would be plugged into something like wall sockets. The fuel cells on the cars could power the local electrical power grid, instead of the grid providing electricity. According to one estimate, only 4 percent of hydrogen fuel cell-powered cars working in this fashion could provide enough power for an entire city.

The impact of major hydrogen use would be even greater on countries that were underdeveloped or undeveloped. Especially if hydrogen is made with a renewable fuel resource such as solar or wind power, energy could be easily accessible to every country on Earth. Developing countries would have better, easier access to electricity and other forms of energy. They could make their own hydrogen energy rather than importing oil to use in generating electricity. The hydrogen economy could better the lives and economies of everyone as local industries spring up, jobs are created, and opportunities abound for social and economic improvement.

In addition to making the United States and other countries less dependent on nonrenewable sources of energy such as oil, hydrogen fuel cell-powered cars in particular could affect noise pollution. Because fuel cell-powered vehicles are very quiet, the familiar sounds of gasoline-powered internal combustion engines would be gone. Urban noise pollution in particular would be greatly lessened, providing a more peaceful environment.

On the other hand, there are a number of safety issues related to the implementation of hydrogen. One problem is that when hydrogen burns, the flame is invisible. In other words, the fire produced by hydrogen is hard to see. The gas itself can also leak out without being detected. Any build up of gas could lead to dangerous explosions, because, although hydrogen is very light weight, is diffuses rapidly. These issues have to be addressed. The first problem could be solved by adding something to the gas so it burns in a way that people can see. One way to solve the second problem is by creating warning instruments that can detect hydrogen gas leaks in the container or the supply chain. Also, colorants can be added to the hydrogen so that the leaks are more easily noticed.

FUTURE TECHNOLOGY

The future of hydrogen as a fuel source might include power plants based on hydrogen technology. Other means of transportation might also benefit from the use of hydrogen as a fuel. For example, planes could take advantage of the fact that hydrogen weighs less than conventional fuels.

Some researchers believe that hydrogen fuel cell-powered generators will be implemented before cars using that technology become widespread. In a 2004 article in Scientific American, Matthew L. Wald noted, "Although most people may have heard of fuel cells as alternative power sources for cars, cars may be the last place they'll end up on a commercial scale." Instead, Wald and others believe that consumer products such as laptop computers, video cameras, and cell phones could be among the first items to be powered by hydrogen fuel cells. Fuel cells are also expected to provide electricity for homes and businesses. Hydrogen fuel cells could potentially provide a source of electric power for electric utilities and in power plants.

For hydrogen fuel cells to become a cornerstone of the hydrogen economy, technological advances must make them cheaper to produce and more powerful when in operation. For example, scientists are working on ways to lessen the need for the platinum catalysts used in PEM fuel cells. Platinum is an expensive precious metal that can add to the cost of building a fuel cell.

CONCLUSION

There are many technological and economic hurdles to adopting hydrogen as an alternative energy source. Still, many experts believe that hydrogen will be the primary energy source of the twenty-first century and beyond. Perhaps more than any other alternative technology that currently exists, hydrogen has the potential to replace our dependence on fossil fuels with a clean source of energy that will never run out.

For More Information

Books

Ewing, Rex. Hydrogen: Hot Cool ScienceJourney to a World of the Hydrogen Energy and Fuel Cells at the Wassterstoff Farm. Masonville, CO: Pixy-jack Press, 2004.

Rifkin, Jeremy. The Hydrogen Economy. New York: Tarcher/Putnam, 2002.

Romm, Joseph J. The Hype of Hydrogen: Fact and Fiction in the Race to Save the Climate. Washington, DC: Island Press, 2004.

Periodicals

Behar, Michael. "Warning: The Hydrogen Economy May Be More Distant Than It Appears." Popular Mechanics (January 1, 2005): 64.

Burns, Lawrence C., J. Byron McCormick, and Christopher E. Borroni-Bird. "Vehicles of Change." Scientific American (October 2002): 64-73.

Graber, Cynthia. "Building the Hydrogen Boom." OnEarth (Spring 2005): 6.

Grant, Paul. "Hydrogen Lifts Offwith a Heavy Load." Nature (July 10, 2003): 129-130.

Guteral, Fred, and Andrew Romano. "Power People." Newsweek (September 20, 2004): 32.

Hakim, Danny. "George Jetson, Meet the Sequel." New York Times (January 9, 2005): section 3, p. 1.

Lemley, Brad. "Lovin' Hydrogen." Discover (November 2001): 53-57, 86.

Lizza, Ryan. "The Nation: The Hydrogen Economy; A Green Car That the Energy Industry Loves." New York Times (February 2, 2003): section 4, p. 3.

McAlister, Roy. "Tapping Energy from Solar Hydrogen." World and I (February 1999): 164.

Muller, Joann, and Jonathan Fahey. "Hydrogen Man." Forbes (December 27, 2004): 46.

Port, Otis. "Hydrogen Cars Are Almost Here, but There Are Still Serious Problems to Solve, Such As: Where Will Drivers Fuel Up?" Business Week (January 24, 2005): 56.

Service, Robert F. "The Hydrogen Backlash." Science (August 13, 2004): 958-961.

Terrell, Kenneth. "Running on Fumes." U.S. News & World Report (April 29, 2002): 58.

Wald, Matthew L. "Questions about a Hydrogen Economy." Scientific American (May 2004): 66.

Westrup, Hugh. "Cool Fuel: Will Hydrogen Cure the Country's Addiction to Fossil Fuels?" Current Science (November 7, 2003): 10.

Westrup, Hugh. "What a Gas!" Current Science (April 6, 2001): 10.

Web Sites

"Driving for the Future." California Fuel Cell Partnership. http://www.cafcp.org (accessed on August 8, 2005).

"How the BMW H2R Works." How Stuff Works.http://auto.howstuffworks.com/bmw-h2r.htm (accessed on August 8, 2005).

"Hydrogen, Fuel Cells & Infrastructure Technologies Program." U.S. Department of Energy Energy Efficiency and Renewable Energy. http://www.eere.energy.gov/hydrogenandfuelcells/ (accessed on August 8, 2005).

"Hydrogen Internal Combustion." Ford Motor Company. http://www.ford.com/en/innovation/engineFuelTechnology/hydrogenInternal-Combustion.htm (accessed on August 8, 2005).

"Reinventing the Automobile with Fuel Cell Technology." General Motors Company. http://www.gm.com/company/gmability/adv_tech/400_fcv/ (accessed on August 8, 2005).

CD-ROMs

World Spaceflight News. 21st Century Complete Guide to Hydrogen Power Energy and Fuel Cell Cars: FreedomCAR Plans, Automotive Technology for Hydrogen Fuel Cells, Hydrogen Production, Storage, Safety Standards, Energy Department, DOD, and NASA Research. Progressive Management, 2003.

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Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.