Determination of the standard molar enthalpies of formation of PbUO4 and Pb3UO6 by microreaction calorimetry
摘要
The standard molar enthalpies of formation of PbUO4 and Pb3UO6 at 298.15 K have been determined from the measurement of molar enthalpies of dissolution. The molar enthalpies of dissolution of PbUO4, Pb3UO6, PbO and UO3 were measured by dissolving the latter in 4 M HNO3 solution in an isothermal microreaction calorimeter; the enthalpy values obtained from these dissolution experiments are − 105.95 ± 3.30, − 270.01 ± 4.71, − 77.03 ± 3.67 and − 64.16 ± 3.73 kJ mol−1, respectively. Using the enthalpies of dissolution and the standard enthalpies of formation of PbO and UO3 from the literature, the standard enthalpies of formation of PbUO4 and Pb3UO6 were derived to be − 1477.6 ± 6.2 and − 1906.4 ± 7.1 kJ mol−1, respectively. By using the standard molar entropies of formation of PbO and UO3 reported in the literature, the standard molar Gibbs energies of formation of PbUO4 and Pb3UO6 were derived to be − 1371.4 ± 6.2 and − 1749.0 ± 7.1 kJ mol−1, respectively. Measurement of molar enthalpies of dissolution with the help of microreaction calorimetry and derivation of standard molar Gibbs energies of formation have been reported for the first time.