Conformal Ionic Mixtures

Abstract

The excess free energy of mixing of molten reciprocal salt solutions (A+, B+, X—, Y—) has been calculated up to the second order by the perturbation method of Reiss, Katz, and Kleppa. The result is a power series containing integral powers of the ion fractions (concentrations). This demonstrates that mixtures of two salts of the same valence type cannot be considered as a mixture of a salt with a dielectricsolvent. The first term in the series is proportional to the free‐energy change for the reaction AX+BY→AY+BX and is the same as the theory of Flood, Fo/rland, and Grjotheim. The results of the symmetric approximation based upon the quasilattice model are consistent with the first term and one of the second‐order terms. The remaining second‐order terms are related to the excess free energy of mixing in the binary systems AX—AY, BX—BY, AX—BX, AY—BY and are of a form first suggested by Fo/rland. This theory, thus, gives a relatively rigorous justification to aspects of previous theories of reciprocal salt solutions which were based upon restrictive models and assumptions.