Derivation and thermodynamically consistent coupling of a Debye-Hückel type energy to a steric electrolyte model and application to the apparent molar volume and phase boundaries
We derive a Debye-Hückel-like model of the electric ion-ion interaction for non-constant dielectric susceptibility, which does not depend on any kind of charging process due to its foundation in the general framework of non-equilibrium electro-thermodynamics. The derivation, however, leads to a novel thermodynamic consistency condition for the temperature dependence of the susceptibility. Due to its contributions to the total pressure, the consistent coupling of this new contribution to the free energy requires subtle modifications in the derivation of the simple mixture model for electrolytes. The coupled model is then applied to the apparent molar volume for various related monovalent salts over a wider range of salt concentrations and temperatures, and classical tests of the electrolyte theory at phase boundaries are investigated.