Thermodynamics of cadmium halide complex formation in acetamide - Calcium nitrate tetrahydrate melt

Abstract

The complex formation between cadmium(II) ions and chloride and bromide ions in the melt of 0.8CH(3)CONH(2)-0.2Ca(NO3)(2). 4H(2)O has been studied at six temperatures between 30 and 80 degrees C. The formation constants of the complexes CdX+ and CdX2 (X-Cl Br) were determined from emf measurements by means of Ag/AgX electrodes. The thermodynamic parameters Delta H(mn)degrees, and Delta S(mn)degrees, for the stepwise complex formation CdmXn-12m-n + X(-)reversible arrow CdmXn2m-n have been estimated. The results are Delta H(11)degrees = 4.2 kJ mol(-1), Delta S(11)degrees = 52.4 J K-1 mol(-1), Delta H(12)degrees = 3.3 kJ mol(-1), Delta S(12)degrees = 40.7 J K-1 mol(-1) for the chloride complexes and Delta H(11)degrees = -3.3 kJ mol(-1), Delta S(11)degrees -33.0 J K-1 mol(-1), Delta H(12)degrees = -2.5 kJ mol(-1), Delta S(12)degrees = 30.4 J K-1 mol(-1) for the bromide complexes. The parameters are compared with the literature data for the same process in dilute aqueous solutions and in some hydrated salt melts. (C) 1999 Elsevier Science B.V. All rights reserved.