Thermodynamics of the zinc sulphide transformation, sphalerite → wurtzite, by modified entrainment

Abstract

The dissociative sublimation of both α- and β-zinc sulphide, ZnS(c)= Zn(g)+½S₂(g), has been studied by modified entrainment in the temperature range 1010–1445 K. The following free-energy equations were derived: ΔG°(α)/J mol^–1= 376 700 – 191.9T/K and ΔG°(β)/J mol^–1= 374 200 – 190.4T/K from which the enthalpy and entropy changes of transformation (β→α) at the transition temperature (1293 K) were –2.5 ± 1.5 kJ mol^–1 and –1.5 ± 1.3 J K^–1 mol^–1. The corresponding ΔH°(β→α) at 298.15 K obtained by the third-law method was –2.3 ± 0.9 kJ mol^–1. This enthalpy change is at variance with the currently accepted value of ca. 13 kJ mol^–1.