Study of experimental-to-McMillan–Mayer conversion of thermodynamic excess functions

Abstract

The problem of the conversion of excess thermodynamic functions, namely the osmotic coefficient and the mean activity coefficient, from the so-called Lewis–Randall (experimental) system to the McMillan–Mayer system has been reconsidered. This correction should be used whenever departures from ideality in ionic solutions are interpreted at the McMillan–Mayer level, in the framework of the primitive model in which the solvent is regarded as a continuum. New general equations and simple approximate expressions have been derived. The latter formulae yield fairly accurate results for the variety of salts considered. Moreover, an important property of these relationships is that they satisfy the Gibbs–Duhem equation. It is found that the corrections caused by the conversion can be significant for concentrations typically above 0.5–1 mol kg–1.