Thermochemistry of uranium compounds. XII. Standard enthalpies of formation of the α and β modifications of uranium pentafluoride. The enthalpy of the β-to-α transition at 298.15 K

Article abstract of DOI:10.1016/0021-9614(82)90050-7

A solution-calorimetric determination of the enthalpies of reaction of the α and β modifications of UF5 with Ce(SO4)2 + H2SO4 is described.Auxiliary measurements were made of the enthalpies of reaction of UO2, γ-UO3, and HF(aq).From these results are calculated the standard enthalpies of formation ΔH⁰_f(298.15 K) of β-UF5, -(2083.0 +/- 6.3) kJ/mol and of α-UF5, -(2075.5 +/- 6.7) kJ/mol.The enthalpy of the (β-to-α) transition is (7.5 +/- 2.1) kJ/mol at 298.15 K.Suggested ΔH⁰_f values are also given for U4F17 and U2F9.