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Is the Reaction Equilibrium Composition in Non-ideal Mixtures Uniquely Determined by the Initial Composition?

Šefčík, Ján (1998) Is the Reaction Equilibrium Composition in Non-ideal Mixtures Uniquely Determined by the Initial Composition? Journal of Chemical Education, 75 (5). pp. 587-588. ISSN 0021-9584. http://resolver.caltech.edu/CaltechAUTHORS:20180801-081916116

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Abstract

Reaction equilibrium can be mathematically described by the equilibrium equation and the reaction equilibrium composition can be calculated by solving this equation. It can be proved by non-elementary thermodynamic arguments that for a generic system with given initial composition, temperature and pressure there is a unique stable equilibrium state corresponding to the global minimum of the Gibbs free energy function. However, when the concept of equilibrium is introduced in undergraduate chemistry and chemical engineering courses, such arguments are generally not accessible. When there is a single reaction equilibrium among mixture components and the components form an ideal mixture, it has been demonstrated by a simple, elegant mathematical argument that there is a unique composition satisfying the equilibrium equation. It has been also suggested that this particular argument extends to non-ideal mixtures by simply incorporating activity coefficients. We show that the argument extension to non-ideal systems is not generally valid. Increasing non-ideality can result in non-monotonicity of the function crucial for the simple uniqueness argument, and only later it leads to non-uniqueness and hence phase separation. The main feature responsible for this is a composition dependence of activity coefficients in non-ideal mixtures.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1021/ed075p587DOIArticle
Additional Information:© 1998 American Chemical Society.
Record Number:CaltechAUTHORS:20180801-081916116
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180801-081916116
Official Citation:Is the Reaction Equilibrium Composition in Non-ideal Mixtures Uniquely Determined by the Initial Composition? Jan Sefcik. Journal of Chemical Education 1998 75 (5), 587. DOI: 10.1021/ed075p587
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88422
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:01 Aug 2018 16:19
Last Modified:01 Aug 2018 16:19

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