Thermochemical study of the molecule BaC2

The enthalpy of the reaction Ba(g)+2C(graph.)=BaC2(g) has been determined by Knudsen effusion mass spectrometry over a barium alloy with noble metals contained in a graphite cell. The value ΔH○0 =252.5± 11.5kJ mol−1 has been obtained from second- and third-law evaluations of the equilibrium vapor in the temperature range 1778–2286 K. This reaction enthalpy has been combined with ancillary literature data to derive the following thermodynamic properties in kJ mol−1 of gaseous BaC2: the atomization energy, ΔatH○0 , 1180.9±12.2; the standard heat of formation, ΔfH○298 , 437.1±14.2; the enthalpy of sublimation of BaC2(s), ΔsubH○298 , 511.2±17.1; and the bond dissociation energy, D○0 (Ba–C2), 581.7±14.8. The results are discussed with regard to their possible significance in reactor technology.