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Effect of a Perturbation on the Chemical Equilibrium: Comparison with Le Châtelier's Principle

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Emilio Martínez Torres

Departament of Physical Chemistry, Escuela de Magisterio, University of Castilla-La Mancha, Ronda de Calatrava 3, 13003 Ciudad Real, Spain

J. Chem. Educ., 2007, 84 (3), p 516

DOI: 10.1021/ed084p516

Publication Date (Web): March 1, 2007

Section:

History, Education, and Documentation

Abstract

This article develops a general thermodynamic treatment to predict the direction of shift in a chemical equilibrium when it is subjected to a stress. This treatment gives an inequality that relates the change in the perturbed variable and the change that the equilibrium shift produces in the conjugated variable. To illustrate the generality of this approach, it has been applied to predict the direction of shift caused by changes of pressure, volume, and amount of substance. In this last case, the well-known unexpected shift in the ammonia synthesis equilibrium upon addition of nitrogen is easily explained. From the above referred inequality and the stability criteria of thermodynamics some conclusions have been obtained about the direction of shift in terms of extensive and extensive variables. This article is suitable for physical chemistry courses.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Physical Chemistry

Keywords (Pedagogy):

Textbooks / Reference Books

Keywords (Subject):

Equilibrium

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Citing Articles

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This article has been cited by 2 ACS Journal articles (2 most recent appear below).

The Adverse Effects of Le Châtelier's Principle on Teacher Understanding of Chemical Equilibrium
Derek Cheung
Journal of Chemical Education2009 86 (4), 514
- The Adverse Effects of Le Châtelier's Principle on Teacher Understanding of Chemical Equilibrium
  Derek Cheung
  Journal of Chemical Education2009 86 (4), 514
  Although the scientific inadequacy of Le Châtelier's principle has long been documented in the literature, the principle is still treated as a central concept of chemical equilibrium by textbook writers and teachers in many countries. In the past, ...
  Abstract | Hi-Res PDF | PDF w/ Links
Comment on "Effect of a Perturbation on the Chemical Equilibrium: Comparison with Le Châtelier's Principle"
Mark J. Uline and David S. Corti
Journal of Chemical Education2008 85 (8), 1052
- Comment on "Effect of a Perturbation on the Chemical Equilibrium: Comparison with Le Châtelier's Principle"
  Mark J. Uline and David S. Corti
  Journal of Chemical Education2008 85 (8), 1052
  In a recent article, Torres presents a thermodynamic analysis of the response of a system initially at chemical equilibrium to an infinitesimal perturbation. While the analysis is correct in this context, Torres argues incorrectly that the general rule so ...
  Abstract | Hi-Res PDF | PDF w/ Links