Atomization energies of the gaseous molecules LaC and La sub 2 C by high-temperature equilibrium measurements

The Knudsen effusion mass spectrometric technique has been used to determine the thermodynamic properties of the molecules LaC and La{sub 2}C. The enthalpies of the reactions La(g) + C(graphite) = LaC(g) and 2La(g) + C(graphite) + La{sub 2}C(g) were measured in two runs in the temperature ranges 2286-2609 and 2767-2835 K, respectively, resulting in {Delta}H{sub 0}{degree} (reaction 1) = 253 {plus minus} 18 kJ mol{sup {minus}1} and {Delta}H{sub 0}{degree} (reaction 2) = -234 {plus minus} 25 kJ mol{sup {minus}1}. From these values the atomization energies, {Delta}H{sub a}{degree}{sub 0}, and standard heats of formation, {Delta}H{sub f}{degree}{sub 298.15}, were obtained as 458 {plus minus} 20 and 685 {plus minus} 20 and 685 {plus minus} 20 kJ mol{sup {minus}1} for LaC and 945 {plus minus} 28 and 625 {plus minus} 28 kJ mol{sup {minus}1} for La{sub 2}C.