Phase equilibrium and activity coefficients in ternary systems at 298.15 K: RbCl/CsCl + ethylene carbonate + water

The (solid   +   liquid) equilibrium (SLE) and (liquid   +   liquid) equilibrium (LLE) of RbCl/CsCl   +   ethylene carbonate (EC)   +   H 2 O ternary systems were carefully investigated at 298.15   K. The SLE and LLE data were correlated by the corresponding equations respectively. Furthermore, the thermodynamic properties of RbCl/CsCl in the EC–water systems were determined by potentiometric method at T   =   298.15   K. The experiment data were correlated by the Pitzer, modified Pitzer and the extended Debye–Hückel equations. The mean activity coefficients, osmotic coefficients and excess Gibbs free energies, standard Gibbs free energy of transfer and the standard solubility product of systems were calculated. The mean activity coefficient γ ± decreases with the increase of the molality of electrolyte at the fixed mass fraction of EC. But γ ± vary abnormally with the increase of the EC content. The result of Δ G t 0 reflects the spontaneously transfer of the electrolytes from water to the mixed solvents.