Thermodynamic investigations on chalcopyrite

The vapor pressures of sulfur in equilibrium with various compositions within the Cu?Fe?S system were measured by a molecular absorption technique. Measurements were made as functions of temperature for the single phase compositions CuFeS_1.62, CuFeS_1.70, CuFeS_1.80 and CuFeS_1.90, for the two-phase fields bornite+chalcopyrite and pyrrhotite+chalcopyrite, and for the three-phase field chalcopyrite+bornite+pyrite. Statistical mechanical equations are derived and used to evaluate the data. Chalcopyrite highly deficient in sulfur behaves similarly to an ideal mixture of Cu₂S and FeS with a random distribution of the constituent cations. Calculated values are given for the Gibbs energy of formation of chalcopyrite at 973 K for compositions CuFeS_1.62 to CuFeS₂, and the entropies and Gibbs energies of formation for CuFeS₂(s) from 800 to 1000 K. Standard entropies, enthalpies, and energies are derived: S⁰ _{CUFeS 2} (298)=32 e.u., ΔH⁰ _{CuFeS 2},f(298)=?42,116 cal, ΔG⁰ _{CuFeS 2} f (298)=?42,800 cal.