Compensation Between the Entropic and Enthalpic Changes Arising from Changes in Solvent-Solvent Interactions in Mixed Solvents

摘要

A theorem presented by Professor Ben-Naim (J Phys Chem 82:874-885, 1978) states that the standard state enthalpy and entropy changes arising from changes in the solvent structure that are induced by solvation of a solute cancel exactly in the standard state Gibbs energy. In this paper this is explored by consideration of the thermodynamics of transfer of electrolytes in mixed solvents, using previously developed models of the solvation process. Two cases are considered. One is random solvation, where curvatures in plots of the transfer enthalpies and entropies, which arise from changes in solvent-solvent interactions, exactly compensate in the transfer Gibbs (free) energies, which are sensibly linear with solvent composition. The second type of system are those with strong preferential solvation where it is found that the transfer Gibbs energies can be accounted for quantitatively in terms of changes in the solute-solvent interactions, with no contribution from changes in solvent-solvent interactions. The results are entirely consistent with the Ben-Naim theorem.