Solute interactions in multicomponent solutions

Abstract

The mathematical formalism for description of solute interactions in dilute, multicomponent solutions should be consistent with (a) the Gibbs-Duhem relations and associated thermodynamic definitions and (b) the principle of regularity of dilute solutions due primarily to Darken. Wagner's original suggestion that Inγ _i and Inγ _j be represented by Taylor's series expansions, withε _i ^(j) = ε_j ⁽ⁱ⁾, meets both these criteria if and only if both first and second order terms are included, with second order coefficients equal to the negatives of the first order coefficients, as in the Darken quadratic formalism. The resulting Wagner-Darken quadratic formalism can be modified for better fit to some experimental data, without loss of rigor, by different choices of components and different definitions of activity coefficients. The recent conjectures of Sukiennik and Olesinski about the thermodynamic validity of the original Wagner formalism are addressed briefly.