Gibbs energy of formation of thorium molybdate (ThMo 2O 8) by the transpiration technique

Abstract

The Gibbs energy of formation of ThMo 2O 8 (s) was determined from its vapour pressure measured by the transpiration technique. ThMo 2O 8(s) vapourized incongruently according to the reaction nThMo 2O 8(s)= nThO 2(s)+2(MoO 3) n (g), n=3, 4 and 5. The Gibbs energy of formation of ThMo 2O 8(s) derived from the vapour pressure of (MoO 3) 3 could be expressed by the relation Δ f G°=−2682.6 + 0.595T ± 12.8 kJ mol −1 (1195⩽ T/K⩽1291.5). The standard enthalpy of formation (Δ f H°298.15 K) of solid ThMo 2O 8 derived from the enthalpy of formation at the mean temperature of the measurements using estimated values for the heat capacity of the compound was found to be Δ f H°=−(2737.4 ± 15.0) kJ mol −1 at 298 K.