Thermodynamics of cadmium-halide—sodium-halide and lead-halide—sodium-halide molten mixtures by emf measurements

Abstract

Molten binary mixtures CdCl 2NaCl, CdI 2NaI, PbCl 2NaCl, PbBr 2NaBr, and PbI 2NaI are studied by means of emf measurements on galvanic cells. In these cells Pyrex glass functions as a sodium indicator electrode. Excess free enthalpies of mixing at 600°C have been calculated from the emf measurements. The excess free enthalpy of mixing of all five mixtures under consideration is negative. The cadmium mixtures show stronger deviations from ideal mixing behaviour than the corresponding lead mixtures and the absolute value of the excess free enthalpy of mixing increases in the sequence iodide-bromide-chloride. From the free enthalpy data and literature values for the enthalpy of mixing, CdCl 2NaCl has a nearly ideal entropy of mixing, whereas PbCl 2NaCl has an appreciable positive excess entropy of mixing. It is shown that the emf values are consistent with differences in theoretical emf's of formation cells.