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The A to G of Chemical Equilibrium: Aspects Depicted by Helmholtz Energy Using Its Relationship to Gibbs Energy

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Arthur E. Burgess

School of Contemporary Sciences, University of Abertay Dundee, Dundee DD1 1HG Scotland

J. Chem. Educ., 2003, 80 (12), p 1476

DOI: 10.1021/ed080p1476

Publication Date (Web): December 1, 2003

Section:

History, Education, and Documentation

Abstract

The approach to chemical equilibrium at constant V, T is considered for various heterogeneous reactions and processes. Analysis is made showing how A and G conveniently interrelate enabling typical 2-D and 3-D Helmholtz energy curves to be drawn across a range of T to illustrate water vaporization and the thermal decomposition of calcium carbonate and ammonium chloride solids. A dip in free energy forms when gas component(s) change in pressure and amount as each reaction proceeds. Equilibrium is consequently attained by the opposing influence of these changes bringing the free energy to a minimum or the entropy to a corresponding maximum. Significantly this effect does not depend on a contribution from a free energy (or entropy) of mixing. The Helmholtz energy curves for the decomposition of ammonium chloride into ammonia and hydrogen chloride are obtained by using (equilibrium) vapor pressures for this two-gas formation and the effect of adding more of one of these gases is allowed for and depicted in comparison plots.

Keywords (Audience):

Upper-Division Undergraduate

Keywords (Domain):

Physical Chemistry

Keywords (Feature):

Research: Science and Education

Keywords (Subject):

Equilibrium

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction
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Journal of Chemical Education2006 83 (7), 1090
- Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction
  Joel Tellinghuisen
  Journal of Chemical Education2006 83 (7), 1090
  Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other ...
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