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

The apparent molal heat capacities ( φ C p ) of 1−1 electrolytes at 25 °C have been fitted to the Pitzer equation φ C p = C̄ p,2 ° + ( A J /1.2) ln(1 + 1.2 I 1/2 ) − 2 RT 2 [ mB J MX + m 2 C J MX ], where C̄ p,2 ° is the partial molal heat capacity of at infinite dilution and B J MX and C J MX are empirical constants related to ion−ion interactions. The values of C̄ p,2 ° of the electrolytes have been used to determine partial molal heat capacities of ions. The coefficients B J MX and C J MX 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%.