Modeling Heat Capacities of High Valence-Type Electrolyte Solutions with Pitzer's Equations

Abstract

Apparent molar heat capacities C p,φ for 71 rare earth chlorides, nitrates, and perchlorates, alkaline earth and transition metal chlorides, nitrates, and perchlorates, and alkali metal carbonates and sulfates have been fitted to the Pitzer equation for heat capacities. The apparent molar heat capacities at infinite dilution $$C_{{\text{p,}}\Phi }^{\text{o}} $$ (equal to the standard partial molar heat capacity, $$\overline C _{{\text{p,2}}}^{\text{o}} $$ ) were used to evaluate a set of “best” ionic heat capacities, from which improved values of $$C_{{\text{p,}}\Phi }^{\text{o}} $$ for the electrolytes were calculated. These were then used in the Pitzer equation to reevaluate the higher Pitzer coefficients. The Pitzer coefficients so evaluated can express, in most cases, the behavior of C p,φ within experimental error from infinite dilution to the upper limit of the data. Ionic heat capacities have been correlated with the absolute entropies of the ions by statistically assigning the ionic heat capacities to obtain the best linear fit.