Thermodynamic consistency and reference scale conversion in multisolvent electrolyte solutions

The conversion of activity coefficients and osmotic coefficients between th e McMillan-Mayer (MM) framework (comprising most electrolyte theories) and the the Lewis-Randall (LR) framework (including most experimental data) is carefully investigated. Two methodologies are presented: (1) the conversion based on the Kirk-wood-Buff solution theory, and (2) thermodynamic princip les (e.g., the Poynting correction). We pay special attention to conversion in multisolvent electrolyte solutions, since its theoretical status is not clearly known, and the industrial importance is great. We clarify the rela tion between the single-solvent case and the multisolvent case. Formulas va lid in the farmer may not be valid in the latter, We develop molecular inte rpretations whenever possible. The Gibbs-Duhem relation, basis of thermodyn amic consistency, is analyzed in both the Lewis-Randall and the McMillan-Ma yer frameworks. A new hybrid formula is derived that allows the proper intr usion of MM quantities into the LR picture. Furthermore, we propose the use of the affinity principle (halophilia and halophobia) regarding the solven ts to construct useful equations for solvent activity calculations. (C) 200 0 Elsevier Science B.V. All rights reserved.