Thermochemistry of La 2 O 2 CO 3 decomposition

Thermochemistry in the decomposition of lanthanum dioxycarbonate, La2O2CO3(s), was studied over the temperature region of 773–1190 K. The decomposition reaction can be written as La2O2CO3(s) = La2O3(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 La2O2CO3(s) and La2O3(s) at different temperatures. The temperature dependence of the equilibrium pressure of CO2 thus measured could be given by ln pCO2 (Pa)(±0.22) =− 17 502.2 T + 25.87 (773 ≤ T( K) ≤ 1190) 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 145.5 ± 5. 0k J mol −1 and 119.2 ± 5. 0Jm ol −1 K −1 , respectively. The results are discussed in the light of available thermochemical data of the compound. © 2002 Elsevier Science B.V. All rights reserved.