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  Home > JCE Print > Journal of Chemical Education > Issues > 2003  > October  >
Research: Science and Education
Approaches to the Treatment of Equilibrium Perturbations
Sebastian G. Canagaratna
Department of Chemistry, Ohio Northern University, Ada, OH 45810
Cover
October 2003
Vol. 80 No. 10
p. 1211
Abstract
Perturbations from equilibrium are treated in the textbooks by a combination of Le Châtelier's principle, the comparison of the equilibrium constant K with the reaction quotient Q,and the kinetic approach. Each of these methods is briefly reviewed. This is followed by derivations of the variation of the equilibrium value of the extent of reaction, ξeq, with various parameters on which it depends. Near equilibrium this relationship can be represented by a straight line. The equilibrium system can be regarded as moving on this line as the parameter is varied. The slope of the line depends on quantities like enthalpy of reaction, volume of reaction and so forth. The derivation shows that these quantities pertain to the equilibrium system, not the standard state. Also, the derivation makes clear what kind of assumptions underlie our conclusions. The derivation of these relations involves knowledge of thermodynamics that is well within the grasp of junior level physical chemistry students. The conclusions that follow from the derived relations are given as subsidiary rules in the form of the slope of ξeq, with T, p, et cetera. The rules are used to develop a visual way of predicting the direction of shift of a perturbed system. This method can be used to supplement one of the other methods even at the introductory level.
More Information
*  Citation
 Canagaratna, Sebastian G. J. Chem. Educ. 2003 80 1211.
*  Keywords
 Equilibrium; General Chemistry; Physical Chemistry; Thermodynamics
*  History
 Created:
Last Updated:		 September 2, 2003
February 28, 2005
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