Thermodynamic study of RbX-CdX2-H2O (X=Cl,Br,I) ternary systems at 25 deg C

Water activity in all the concentration range has been studied and thermodynamic potentials of solid compound formation in RbX-CdX2-H2O(X=Cl,Br,I) systems at 25 deg C have been calculated. Water activity was determined by isopiestic method. Measurement results were given as water isoactivate family. Extremely strong curving of isoactivates is indicative of the presence of intensive complexing processes in mixed water solutions of rubidium and cadmium halogenides. Phase equilibrium data were used for the calculations of thermodynamic potential changes at the formation of solid complexes in systems; they have the following values expressed in kcal/mol: for RbClxCdCl2-ΔG=-7.08; for 4RbClxCdCl2-ΔG=-10.77; for RbBrxCdBr2-4.88; for 4RbBrxCdBr2--7.44; for RbIxCdI2xH2O--3.05; for 5/3RbIxCdI2--3.48. Thus the thermodynamic potential change at the formation of the solid complex compounds in the given systems increases in the following order: I<Br<Cl