An investigation of the thermodynamic properties of cadmium sulphide

Abstract

The free energy of formation of cadmium sulphide has been determined by an electrochemical technique using a molten salt electrolyte (LiCl-KCl+5 wt.% CdCl2) galvanic cell. From the open circuit e.m.f. of the galvanic cell measured at different temperatures the ΔG⊖ versus T relationship for the reaction Cd(l)+S(l) = CdS(s) has been established: ΔG⊖ =(-164.295+31.37T) ±310 J mol-1 (640 < T< 690 K). The enthalpy of formation was measured directly in a differential thermal analysis calorimeter. For these investigations, the values of ΔG⊖298, ΔH⊖298 and ΔS⊖298 were calculated as -149.8 ±2.0 kJ mol-1, -153.3 ± 2.8 kJ mol-1, -11.7 JK-1 mol-1 and 72.0 JK-1 mol-1, respectively. The estimated values of the lattice constants (based on the covalent, rationalised and ionic radii of cadmium and sulphur), the enthalpy of formation (based on Pauling's and Phillips' methods) and the standard entropy (based on Latimer's method) are compared with the experimental values and discussed with reference to the structure and bonding. © 1992.