Solubility of RbCl and CsCl in pure water at subzero temperatures, heat capacity of RbCl(aq) and CsCl(aq) at T = 298.15 K, and thermodynamic modeling of RbCl + H2O and CsCl + H2O systems

Solubility of RbCl(cr) and CsCl(cr) in pure water were determined at subzero temperatures. The solubility of RbCl(cr) and CsCl(cr) decreased with temperature increment. Specific heat capacity of RbCl(aq) and CsCl(aq) solutions were determined at 298.15   K and concentration to near saturation. The specific heat capacity of RbCl(aq) and CsCl(aq) solutions decreased with concentration increment and for the same molality the specific heat capacity of CsCl(aq) is smaller than that of RbCl(aq). A temperature dependent thermodynamic model based on the Pitzer-Simonson-Clegg activity coefficient equations was used to represent the activity, thermal and solid-liquid equilibria properties of RbCl   +   H 2 O and CsCl   +   H 2 O systems. The obtained models can reproduce and predict the thermodynamic properties and phase diagram of the two binary systems well for the temperature range from 200   K to 370   K. The present models have an advantage especially at subzero temperatures due to the utilization of low temperature solubility experimental data in parameterization.