Electrochemical determination of the thermodynamic parameters of sphalerite, ZnS

Thermodynamic properties of sphalerite (β-ZnS, F4-3m) were studied by the method of high-temperature galvanic cell with separate gas space and Y₂O₃-stabilized ZrO₂ as solid-state electrolyte. The temperature dependences of the cell electromotive force (EMF) were obtained for the reaction ZnS + 2Ag + NiO=ZnO + Ag₂S + Ni in the temperature range 782-1050 K, and for the reaction ZnS + 2Cu + NiO = ZnO + Cu₂S + Ni in the temperature range 848-1288 K. The standard parameters of sphalerite were analyzed by the second law of thermodynamics. The standard enthalpy of formation of ZnS, Δ_fH^o _ZnS(298 K) = -201.07 ± 1.3 kJ mol^-1, was calculated for the reaction Zn_(s) + S_(s) = ZnS_(β) using the third law of thermodynamics (Gef method) and data on standard enthalpy of formation for ZnO, NiO, Ag₂S, and Cu₂S. From the EMF results for the ZnS/ZnO equilibrium and using the known data on free energy of formation of ZnO, NiO, Ag₂S and Cu₂S, the free energy of sphalerite formation was found according to the reaction Zn_(l) + 0.5S_2(g) = ZnS_(β): Δ_fG_ZnS^o(T) ± 1000 J mol^-1 = -273, 870 + 107.30 · T, (782 < T/K < 1050),(logfS₂ > -9) Δ_fG_ZnS^o(T) ± 1300 Jmol^-1= -268, 892 + 102.67 · T, (848 < T/K < 1180),(log fS₂ < -9) Similarly, for the reaction Zn_(g)+0.5S_2(g)=ZnS_(β): Δ_fG_ZnS^o(T) ±(T) ± 1300 J mol^-1= -382,203+198.75 · T, (1180 < T/K < 1293) The obtained results were compared to the literature data.