Uniqueness of chemical equilibria in ideal mixtures of ideal gases

摘要

We prove the uniqueness of chemical equilibrium for an ideal mixture of ideal gases in a closed, spatially homogeneous volume. Uniqueness, a fundamental issue of chemical physics, is incompletely justified in textbooks and much of the scientific literature. We first reproduce a little known proof by Zel'dovich and show in a more direct fashion than originally presented that a unique equilibrium exists for isothermal reactions. Zel'dovich's approach is then extended to the adiabatic case, and a more complete exposition than that of Aris is provided. The example of an isothermal, isochoric O-O-2-O-3 system provides an illustration of uniqueness. The discussion should be useful for students and instructors of graduate level thermal physics, as well as for researchers in macroscale reaction dynamics. (C) 2008 American Association of Physics Teachers.