chemical equilibrium

Home > ... > Science and Technology > Chemistry > Chemistry: General > ...

chemical equilibrium

The Columbia Encyclopedia, Sixth Edition | 2008 | The Columbia Encyclopedia, Sixth Edition. Copyright 2008 Columbia University Press. (Hide copyright information) Copyright

chemical equilibrium state of balance in which two opposing reversible chemical reactions proceed at constant equal rates with no net change in the system. For example, when hydrogen gas, H 2 , and iodine gas, I 2 , are mixed, and gaseous hydrogen iodide, HI, is formed according to the equation H 2  + I 2  → 2HI, no matter how long the reaction is allowed to proceed some quantity of hydrogen and iodine will remain unreacted. The reason reactants in a reversible reaction are never completely converted to product is that an opposing reaction is taking place simultaneously, i.e., some of the newly formed HI is being converted back into hydrogen and iodine. For any particular temperature, a point of equilibrium is reached at which the rates of the two opposing reactions are equal and there is no further change in the system. This equilibrium point is characterized by specific relative concentrations of reactants and products and will also be reached from the opposite direction, i.e., if one starts with hydrogen iodide and allows it to decompose into hydrogen and iodine. The equilibrium point can be described by the mass action expression, which defines the equilibrium constant, Keq , in terms of the ratio of the molar concentrations of the products to those of the reactants. For the reversible reaction used as an example, the equilibrium constant is Keq =[HI] 2 /[H 2 ][I 2 ]; for the general reversible reaction n A +  m B + · · · [double arrow]   p C +  q D + · · · , the equilibrium constant is: where [A], [B], [C], [D], … are the molar concentrations of the substances and n, m, p, q,  … are the coefficients of the balanced chemical equation. The larger the equilibrium constant for a given reaction, the more the reaction is favored, since a larger value of Keq means larger concentrations of the products relative to the reactants. The equilibrium constant is related to the change in the standard free energy, G °, of the system by the equation Δ G ° = - RT. ln Keq , where R is a constant, T is the temperature in degrees Kelvin, and ln Keq is the natural logarithm of the equilibrium constant. Chemical equilibrium can be defined for many types of chemical processes, such as dissociation of a weak acid in solution, solubility of slightly soluble salts, and oxidation-reduction reactions. In all of these cases, the equilibrium constant or its analogue is defined for certain conditions of temperature and other factors. If any of these factors change, the system will respond to establish a new equilibrium, in accordance with Le Châtelier's principle .

Hide all research tools
Print this article Print all entries for this topic Cite this article Link to this article
Link to this article

CloseClose

Create a link to this page

Copy and paste this link tag into your Web page or blog:

<a href="http://www.encyclopedia.com/topic/.aspx#1E1-chem-equi" title="Facts and information about chemical equilibrium">chemical equilibrium</a>

Add this article to Del.icio.usBookmark this article on DiigoShare this article on FacebookSubmit this article to RedditGive this article a thumbs-up on StumbleUpon
Show all research tools

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"chemical equilibrium." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. 16 Nov. 2009 <http://www.encyclopedia.com>.

"chemical equilibrium." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. (November 16, 2009). http://www.encyclopedia.com/doc/1E1-chem-equi.html

"chemical equilibrium." The Columbia Encyclopedia, Sixth Edition. 2008. Retrieved November 16, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-chem-equi.html

Learn more about citation styles

chemical equilibrium

World Encyclopedia | 2005 | © World Encyclopedia 2005, originally published by Oxford University Press 2005. (Hide copyright information) Copyright

chemical equilibrium Balance in a reversible reaction, when two opposing reactions proceed at constant equal rates with no net change in the system. The initial rate of the reactions falls off as the concentrations of reactants decrease and the build-up of products causes the rate of the reverse reaction to increase. This is seen in the Haber process where ammonia formed by nitrogen and hydrogen immediately breaks down again into those elements.

Hide all research tools
Print this article Print all entries for this topic Cite this article Link to this article
Link to this article

CloseClose

Create a link to this page

Copy and paste this link tag into your Web page or blog:

<a href="http://www.encyclopedia.com/topic/.aspx#1O142-chemicalequilibrium" title="Facts and information about chemical equilibrium">chemical equilibrium</a>

Add this article to Del.icio.usBookmark this article on DiigoShare this article on FacebookSubmit this article to RedditGive this article a thumbs-up on StumbleUpon
Show all research tools

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"chemical equilibrium." World Encyclopedia. 2005. Encyclopedia.com. 16 Nov. 2009 <http://www.encyclopedia.com>.

"chemical equilibrium." World Encyclopedia. 2005. Encyclopedia.com. (November 16, 2009). http://www.encyclopedia.com/doc/1O142-chemicalequilibrium.html

"chemical equilibrium." World Encyclopedia. 2005. Retrieved November 16, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-chemicalequilibrium.html

Learn more about citation styles

Related articles from newspapers, magazines, and more

FactSage and ChemApp: two tools for the prediction of multiphase chemical equilibria in solutions *,**.
Magazine article from: Pure and Applied Chemistry; 6/1/2008; ; 700+ words ; ...enables the user to calculate equilibria and thermodynamic properties...FactSage are of interest to chemical and physical metallurgy, chemical and corrosion engineering...handling of repetitive complex equilibrium calculations in application...leach solutions. Keywords: chemical ...
Recycling of magnesium alloys: Chemical equilibria between magnesium-lithium-based melts and salt melts
Magazine article from: Metallurgical and Materials Transactions; 6/1/2002; ; 700+ words ; ...and salt phases were determined by chemical analyses. The obtained data were evaluated...2LiCl + Ba (Reaction [3]). The equilibrium of Reaction [1] is much on the right...lithium alloys and deals with the chemical equilibria between magnesium-lithium melts and...
FIJACIÓN Y REDUCCIÓN FUNCIONALES COMO RAZONAMIENTOS DE SENTIDO COMÚN EN EL APRENDIZAJE DE LA QUÍMICA (I): EQUILIBRIO QUÍMICO/Fuctional Fixedness and Functional reduction as common sense reasonings in chemistry learning (I): Chemical Equilibrium
Magazine article from: Journal of Science Education; 1/1/2000; ; 700+ words ; ...external factors affecting equilibria (chemical equilibrium) and geometry and polarity...This first paper is about the chemical equilibrium. The incorrect...reduccion, functional fixedness, chemical equilibrium. INTRODUCCIN...
Cequel[R]: chemical equilibrium in Excel.(Engineering Tools)
Magazine article from: Mechanical Engineering-CIME; 4/1/2005; 368 words ; Cequel is an Excel Add-In that solves chemical equilibrium problems as a spreadsheet function. It is based...adiabatic flame temperature, or use it to determine equilibrium states for your own model. www.seainc.com info...
Cequel[R] chemical equilibrium in Excel.(Engineering Tools)
Magazine article from: Mechanical Engineering-CIME; 10/1/2005; 359 words ; Cequel is an Excel Add-In that solves chemical equilibrium problems as a spreadsheet function. It is based...adiabatic flame temperature, or use it to determine equilibrium states for your own model. www.seainc.com info...
Cequel[R]: chemical equilibrium in excel.(Engineering Tools)
Magazine article from: Mechanical Engineering-CIME; 6/1/2005; 368 words ; Cequel is an Excel/Add-In that solves chemical equilibrium problems as a spreadsheet function. It is based...adiabatic flame temperature, or use it to determine equilibrium states for your own model. [GRAPHIC OMITTED...
Molecular-level thermodynamic switch controls chemical equilibrium in sequence-specific hydrophobic interaction of 35 dipeptide pairs
Magazine article from: Biophysical Journal; 2/1/2003; ; 700+ words ; ...hence a maximum in the related equilibrium constant, K^sub eq...entitled "Thermodynamics, Chemical Reactions and Molecular Biology...360 Kelvin show that the "chemical bond" component of the overall...independent component of the chemical bond enthalpy is the inherent...
Prediction of equilibrium solubility of C[O.sub.2] in aqueous alkanolamines using differential evolution algorithm.(R&D NOTE)
Magazine article from: Canadian Journal of Chemical Engineering; 2/1/2008; ; 700+ words ; ...manufacture. Regenerative chemical absorption of the acid gases...knowledge of vapour--liquid equilibrium (VLE) of the acid gas over...mass transfer coupled with chemical reactions. The major problem...brief discussion about the chemical equilibria, vapour--liquid phase...
Phase Equilibria, Phase Diagrams and Phase Transformations: Their Thermodynamic Basis
Magazine article from: Chemical Engineering Progress; 10/1/2008; ; 433 words ; Phase Equilibria, Phase Diagrams and Phase Transformations...covers the theoretical basis of chemical equilibria and chemical engineering, with an emphasis...Theoretical descriptions of equilibrium conditions, the state of systems...
Influence of Calcium Salt Supplementation on Calcium Equilibrium in Skim Milk During pH Cycle
Magazine article from: Journal of Dairy Science; 5/1/2007; ; 700+ words ; ...2003). When subjected to chemical equilibria, Ca partition in milk varies...Protons and Ca ions are in equilibria with their respective phosphate...citrate salts (Brul, 1981). Equilibria are shifted toward the colloidal...
Click to see an enlarged picture
chemical equilibrium. Wikimedia Commons (Public Domain)

For students and teachers!

Encyclopedia.com provides students and teachers facts, information, and biographies from verified, citable sources, including:

Encyclopedia.com provides students and teachers facts, information, and biographies from verified, citable sources, including:

Popular on Newser:

OMG, Enuf With Ur Duckface

(11/15/2009 7:50:02 PM)

Craziest Rap Concert Demands

(11/15/2009 5:30:03 PM)

'The Wasilla Whack-Job' Reads My Blog!

(11/15/2009 10:14:01 PM)

Nation's First Marijuana Cafe Opens in Portland

(11/14/2009 6:19:02 PM)

Obama's Ego Needs Its Own ZIP Code

(11/14/2009 6:01:02 PM)