THERMODYNAMIC TREATMENT AND ELECTROMOTIVE FORCE MEASUREMENTS OF TERNARY MOLTEN SALT SYSTEMS SILVER CHLORIDE-SODIUM CHLORIDE-POTASSIUM CHLORIDE AND SILVER CHLORIDE-SODIUM CHLORIDE-CESIUM CHLORIDE

Partial molar excess free energies of mixing of silver chloride have been determined in the binary systems AgCl-NaCl, AgCl-KCl, and AgCl-CsCl and in the ternary systems AgCl-NaCl-KCl and AgCl-NaCl-CsCl by an electromotive force technique using the reversible formation cell Ag-AgCl + alkali chlorides-Cl2, graphite. The excess free energies for AgCl in the binary systems could be represented by the expression A(1 - NAgCl)2. The parameter A is 900 cal/mol for the AgCl-NaCl system, -1500 cal/mol for the AgCl-KCl system, in accord with prior measurements, and -3450 cal/mol in the AgCl-CsCl system which had not been measured previously. A convenient thermodynamic formalism for the ternary systems is introduced in which the excess free energies are related to weighted sums of the excess free energies of the three binary systems and a ternary term (eq 8). The small ternary terms calculated from our measurements are consistent with calculations of this term from the quasi-lattice theory and illustrate a significant property of ternary systems.