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calorimetry

calorimetry (kăl´ərĬm´ətrē), measurement of heat and the determination of heat capacity. Heat is evolved in exothermic processes and absorbed in endothermic processes; such processes include chemical reactions, transitions between the states of matter, and the mixing of two substances to form a solution (see thermodynamics). A number of different units are used in heat measurement, e.g., the calorie, the British thermal unit (Btu), and the joule. The apparatus used in heat measurement is called a calorimeter. The measurement given by the most common type of calorimeter depends upon the temperature change in a fixed quantity of water (or some other liquid whose heat capacity is known) when heat is transferred between the water and an exothermic or endothermic process. If the temperature change is not too large, then the heat transferred is equal to the heat capacity of the water times the mass of the water times the change in temperature. The accuracy of this method of heat measurement depends on the assumption that all the heat transferred in the process passes into or out of the water in which the temperature change is measured, no heat being lost to the environment and none being absorbed by the walls of the container. The amount of heat given off by the combustion of a fuel can be determined very accurately in the so-called bomb calorimeter, which consists of a combustion chamber (the "bomb" ) set in another chamber filled with water. Heat generated by combustion of the fuel is transmitted to the water, raising its temperature. The calorie content of food is tested this way. Calorimeters are also employed to measure the energies of elementary particles.

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calorimetry

calorimetry The measurement of energy expenditure by the body. Direct calorimetry is the direct measurement of heat output from the body, as an index of energy expenditure, and hence energy requirements. The subject is placed inside a small, thermally insulated room, and the heat produced is measured.

Indirect calorimetry is a means of estimating energy expenditure by either measurement of the rate of oxygen consumption, using a spirometer, (each litre of oxygen consumed is equivalent to 20 kJ energy expenditure) or estimation of the total production of carbon dioxide over a period of 7–10 days, after consumption of dual isotopically labelled water (i.e. water labelled with both 2H and 18O). See also isotopes.

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Calorimetry

Calorimetry

History

The calorimeter

Calorimetry theory

Resources

Calorimetry is the measurement of the amount of heat gained or lost during a physical or chemical change. Heats of fusion or vaporization, heats of solution, and heats of reaction are examples of the kinds of determination that can be made in calorimetry. The term itself derives the Latin word for heat, caloric, as is the name of the instrument used to make these determinations, the calorimeter. Biocalorimetry is the measurement of heat loss and gain in biological processes.

History

Little productive work on the measurement of heat changes was accomplished prior to the mid-nineteenth century for two reasons. First, the exact nature of heat itself was not well understood. Until the work of the Scottish chemist Joseph Black in the late eighteenth century, the distinction between temperature and heat was not at all clear. It then took until about 1845 before the nature of heat as a form of energy and not of matter was made clear in the experiments of James Joule (18181889) and others.

Secondly, given such uncertainties, it is hardly surprising that appropriate equipment for the measurement of heat changes was not available until after the 1850s. Antoine Lavoisier (17431794) and Pierre Laplace (17491827) had made use of a primitive ice calorimeter to measure the heats of formations of compounds in 1780, but their work was largely ignored by their colleagues in chemistry.

In fact, credit for the development of modern techniques of calorimetry should probably be given to the French chemist Pierre Euge`ne Berthelot (18271907). In the 1860s, Berthelot became interested in the problems of heat measurement. He constructed what was probably the first modern calorimeter and invented the terms endothermic and exothermic to describe reactions in which heat is taken up or given off, respectively.

The calorimeter

In essence, a calorimeter is any device in which the temperature before and after some kind of change can be accurately measured. Probably the simplest of such devices is the coffee cup calorimeter, so-called because it is made of a styrofoam cup such as the ones in which coffee is commonly served. A styrofoam cup is used because styrofoam is a relatively good insulating material. Heat given off within it as a result of some physical or chemical change will not be lost to the surrounding environment. To use the coffee cup calorimeter, one simply carries out the reaction to be studied inside the coffee cup, measures the temperature changes that take place, and then calculates the amount of heat lost or gained during the change.

The type of calorimeter more commonly used for precise work is called the bomb calorimeter. A bomb calorimeter designed to measure heat of combustion, as an example, consists of a strong-walled metal container set inside another container filled with water. The inner container is fitted with an opening through which oxygen can be introduced and with electrical leads to which a source of electricity can be connected.

The object to be studied is then placed in a combustion crucible within the bomb and ignited. The reaction occurs so quickly within the reaction chamber that it is similar to the explosion of a bombhence the instruments name. Surrounding the bomb in this arrangement is a jacket filled with (usually) water. Heat given off or absorbed within the bomb heats up the water in the jacket, a change that can readily be measured with a thermometer inserted into the water.

Many variations in the basic design described here are possible. For example, the use of liquids other than water in the insulating jacket can permit the study of heat changes at higher temperatures than the sea-level boiling point of water 212°F (100°C). Aneroid (without liquid) calorimeters are also used for special purposes, such as the measurement of heat changes over very large temperature ranges. Such calorimeters use metals with a high coefficient of thermal conductivity, like copper, to measure the gain or loss of heat in some type of change.

KEY TERMS

Heat The transfer of thermal energy that occurs between two objects when they are at different temperatures.

Insulator An object or material that does not conduct heat or electricity well.

Specific heat The amount of heat needed to increase the temperature of a mass of material by one degree.

Temperature A measure of the average kinetic energy of all the elementary particles in a sample of matter.

Calorimetry theory

Suppose that a cube of sugar is burned completely within the bomb of a calorimeter. How can an experimenter determine the heat released in that reaction?

To answer that question, the assumption is made that all of the heat produced in the reaction is used to raise the temperature of the water in the surrounding jacket and the metalwalls of the bomb itself. The heat absorbed by each is equal to its mass multiplied by its specific heat multiplied by the temperature change (DT). Using a word equation to express this fact: heat released in reaction = (mass of water × specific heat of water × DT) + (mass of bomb × specific heat of bomb × DT). The last part of this equation, (mass of bomb × specific heat of bomb × DT), is the same for any given calorimeter. Once measured, it is known as a constant value and, therefore, is given the name of calorimeter constant.

Resources

BOOKS

The Japan Society of Calorimetry and Thermal Analysis, ed. Comprehensive Handbook of Calorimetry and Thermal Analysis. Hoboken, NJ: John Wiley & Sons, 2004.

David E. Newton

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Calorimetry

Calorimetry

Calorimetry is the measurement of the amount of heat gained or lost during some particular physical or chemical change. Heats of fusion or vaporization, heats of solution , and heats of reaction are examples of the kinds of determination that can be made in calorimetry. The term itself derives the Latin word for heat, caloric, as is the name of the instrument used to make these determinations, the calorimeter.


History

Little productive work on the measurement of heat changes was accomplished prior to the mid-nineteenth century for two reasons. First, the exact nature of heat itself was not well understood. Until the work of the Scottish chemist Joseph Black in the late eighteenth century, the distinction between temperature and heat was not at all clear. It then took until about 1845 before the nature of heat as a form of energy and not of matter was made clear in the experiments of James Joule and others.

Secondly, given such uncertainties, it is hardly surprising that appropriate equipment for the measurement of heat changes was not available until after the 1850s. Lavoisier and Laplace had made use of a primitive ice calorimeter to measure the heats of formations of compounds in 1780, but their work was largely ignored by their colleagues in chemistry .

In fact, credit for the development of modern techniques of calorimetry should probably be given to the French chemist Pierre Eugène Berthelot (1827-1907). In the 1860s, Berthelot became interested in the problems of heat measurement. He constructed what was probably the first modern calorimeter and invented the terms endothermic and exothermic to describe reactions in which heat is taken up or given off, respectively.


The calorimeter

In essence, a calorimeter is any device in which the temperature before and after some kind of change can be accurately measured. Probably the simplest of such devices is the coffee cup calorimeter so-called because it is made of a styrofoam cup such as the ones in which coffee is commonly served. A styrofoam cup is used because styrofoam is a relatively good insulating material. Heat given off within it as a result of some physical or chemical change will not be lost to the surrounding environment. To use the coffee cup calorimeter, one simply carries out the reaction to be studied inside the coffee cup, measures the temperature changes that take place, and then calculates the amount of heat lost or gained during the change.

The type of calorimeter more commonly used for precise work is called the bomb calorimeter. A bomb calorimeter designed to measure heat of combustion , as an example, consists of a strong-walled metal container set inside another container filled withwater. The inner container is fitted with an opening through which oxygen can be introduced and with electrical leads to which a source of electricity can be connected.

The object to be studied is then placed in a combustion crucible within the bomb and ignited. The reaction occurs so quickly within the reaction chamber that it is similar to the explosion of a bomb. Hence theinstrument's name. Surrounding the bomb in this arrangement is a jacket filled with (usually)water. Heat given off or absorbed within the bomb heats up the water in the jacket, a change that can readily be measured with a thermometer inserted into the water.

Many variations in the basic design described here are possible. For example, the use of liquids other than water in the insulating jacket can permit the study of heat changes at higher temperatures than the boiling point of water 212°F (100°C). Aneroid (without liquid) calorimeters are also used for special purposes, such as the measurement of heat changes over very large temperature ranges. Such calorimeters use metals with a high coefficient of thermal conductivity, like copper , to measure the gain or loss of heat in some type of change.


Calorimetry theory

Suppose that a cube of sugar is burned completely within the bomb of a calorimeter. How can an experimenter determine the heat released in that reaction?

To answer that question the assumption is made that all of the heat produced in the reaction is used to raise the temperature of the water in the surrounding jacket and the metalwalls of thebomb itself. The heat absorbed by each is equal to its mass multiplied by its specific heat multiplied by the temperature change (DT). Using a word equation to express this fact: heat released in reaction = (mass of water × specific heat of water × DT) + (mass of bomb × specific heat of bomb × DT). The last part of this equation, (mass of bomb × specific heat of bomb × DT), is the same for any given calorimeter. Once measured, it is known as a constant value and, therefore, is given the name of calorimeter constant.

Resources

books

Asimov, Isaac. Asimov's Biographical Encyclopedia of Science& Technology. 2nd revised edition. Garden City, NY: Doubleday & Company, Inc., 1982, pp. 443-444.

Masterson, William L., Emil J. Slowinski, and Conrad L. Stanitski. Chemical Principles. Philadelphia: Saunders, 1983.


David E. Newton

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Heat

—The transfer of thermal energy that occurs between two objects when they are at different temperatures.

Insulator

—An object or material that does not conduct heat or electricity well.

Specific heat

—The amount of heat needed to increase the temperature of a mass of material by one degree.

Temperature

—A measure of the average kinetic energy of all the elementary particles in a sample of matter.

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"Calorimetry." The Gale Encyclopedia of Science. . Encyclopedia.com. 12 Nov. 2018 <https://www.encyclopedia.com>.

"Calorimetry." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 12, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/calorimetry-0

"Calorimetry." The Gale Encyclopedia of Science. . Retrieved November 12, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/calorimetry-0

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