ENTHALPY OF HYDROLYSIS OF RHENIUM TRICHLORIDE . ENTHALPY AND FREE ENERGY OF FORMATION OF RHENIUM SESQUIOXIDE

The standard enthalpy of hydrolysis of rhenium trichloride in alkaline solution to form hydrated rhenium sesquioxide has been observed to be -54.29 ± 0.14 kcal (gfw of ReCl3)-1 at 25°. This result combined with other available thermal data gives for the enthalpy of formation ΔHf°(Re2O3) = -119.2 kcal mol-1. The entropy of Re2O3 is estimated to be 32 cal deg-1 mol-1 which leads to ΔFf°(Re2O3) = -101.6 ± 0.6 kcal mol-1 for the free energy of formation at 25°. The electrode potentials of the half-reactions 2Re + 6OH- = Re2O3 + 3H2O + 6e- and Re2O3 + 20H- + 3H2O = 2ReO2·2H2O + 2e- are computed to be 0.333 ± 0.004 and 1.25 ± 0.01 V, respectively.