Enthalpy and Gibbs energy of formation of cerium dicarbide

Abstract

The equilibrium CO pressure over the condensed phase region of CeO2 (s)–CeC2 (s)–C(s) was determined by adopting a method termed as the dynamic effusion MS method, which involves the measurement of the CO effusing out from the sample using a quadrupole mass spectrometer, even during carbothermic reduction of the oxide. The formation of oxicarbide has been ruled out. The Gibbs energies of the reaction, CeO2 (s)+4C(s) = CeC2 (s)+2CO(g), at various temperatures in the range 1350–1550 K were then determined from the equilibrium CO pressures. From the Gibbs energies of the reaction, the Gibbs energy of formation of CeC2 (s) at 298 K was derived. Similarly, from the data on the second and third-law enthalpies of the above reaction, the enthalpy of formation of CeC2 (s) at 298 K was calculated. The recommended Gibbs energy and enthalpy of formation of CeC2 (s) at 298 K are (103:0) and (120:1 ) kJ/mol, respectively.