Modeling the Heat Capacities of Aqueous 1−1 Electrolyte Solutions with Pitzer's Equations

The apparent molal heat capacities (φCp) of 1−1 electrolytes at 25 °C have been fitted to the Pitzer equation φCp = Cp,2° + (AJ/1.2) ln(1 + 1.2I1/2) − 2RT2[mBJMX + m2CJMX], where Cp,2° is the partial molal heat capacity of at infinite dilution and BJMX and CJMX are empirical constants related to ion−ion interactions. The values of Cp,2° of the electrolytes have been used to determine partial molal heat capacities of ions. The coefficients BJMX and CJMX have been combined with Pitzer coefficients for enthalpies and osmotic coefficients to develop equations that can be used to determine activity coefficients of these electrolytes from 10 to 70 °C and from 0.1 to 2 m to within 1%.