Enthalpies of formation of Sm 2O 3(monoclinic) and Sm 2O 3(cubic)

Abstract

New measurements of the enthalpy of formation of Sm 2O 3(monoclinic) have been made by oxygen-bomb combustion calorimetry and by solution calorimetry. The weighted average value found is ΔH° t (Sm 2O 3, (monoclinic), 298.15 K) = −(435.86±0.45) kcal th mol −1 From the difference in the enthalpies of solution of Sm 2O 3(monoclinic) and Sm 2O 3(cubic), the enthalpy of transition is found to be ΔH° tr {Sm 2O 3(cubic)=Sm 2O 3(monoclinic), 298.15 K} = (0.9±0.6) kcal th mol −1 and the enthalpy of formation of Sm 2O 3(cubic) is ΔH° t (Sm 2O 3,cubic, 298.15 K) = −(436.76±0.73) kcal th mol −1