Thermochemistry of Gd2O2CO3 decomposition

Thermochemistry in the decomposition of gadolinium di-oxycarbonate, Gd2O2CO3(s), was studied over the temperature region of 774 to 952 K. The decomposition reaction can be written as, Gd2O2CO3(s) = Gd2O3(s) + CO2(g) The equilibrium property of the above reaction was then studied by tensimetric measurement of the CO2(g) pressure over the biphasic mixture of Gd2O2CO3(s) and Gd2O3(s) at different temperatures. The temperature dependence of the equilibrium pressure of CO2 thus measured could be given by ln PCO2/bar (± 0.13) = -22299.0/T + 23.36 (774 ≤ T/K ≤952) From the above vapor pressure expression, the median enthalpy and entropy of the decomposition of the oxycarbonate from the second law analysis worked out to be 185.4 ± 5.0 kJ mol-1 and 194.2 ± 5.0 J K-1 mol-1, respectively. The results are discussed in the light of available thermochemical data of the compound. (author)