Mixing Models and Activity-Composition Relations

Abstract

The functional forms of the expressions of activity coefficients in terms of composition have been developed from both macroscopic and atomistic reasonings. The macroscopic models are derived from considerations of the appropriate forms of ΔG^XS as a function of composition, and operating on these empirical functions according to the relationships between ${\tilde{\gamma }_i}$ and ΔG^XS described in Chapter 1.II. Of these, the most generally useful formulation of ΔG^XS(X) is due to Guggenheim (1937), who suggested the following polynomial form for a binary solution, which satisfies the required property that ΔG^XS = 0 at the end-member compositions.