Calculation of Gibbs free energies of aqueous electrolytes to 350.degree.C from an electrostatic model for ionic hydration

Abstract

An electrostatic model that had previously been developed to describe standard state thermodynamic functions for ionic hydration at 298 K is used to calculate the Gibbs free energy function, anti G/sup 0//sub T/ - anti G/sup 0//sub 298/, for 14 group 1a, 2a, 3a, and 3b cations and the trivalent lanathides and actinides, from 323 to 623K. The calculation employs a temperature independent primary hydration number derived from the entropy of each aquo ion at 298 K as the only adjustable parameter. Above 423 K, the standard state partial molal Gibbs free energies predicted by the model reproduce the available experimental data much more accurately than those calculated by the Criss-Cobble entropy correspondence principle or by assuming that the room temperature heat capacities are invariant with temperature. Results from the model are less reliable above 548 K, presumably because of compressibility effects and variations in the primary hydration number.