Enthalpy and Gibbs energy of formation of cerium dicarbide

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 +/- 6.0) and (120.1 +/- 11.0) kJ mol(-1), respectively. (C) 2003 Elsevier Science B.V. All rights reserved.