Dissociation Energy of Diatomic Cerium and Predicted Stability of Gaseous Intermetallic Cerium Compounds
The Knudsen-cell mass spectrometric method has been used to study gaseous equilibria over the Au–Ce–CeS–BN–C system. The third-law enthalpies, ΔH0°, in kcal mole−1, of the reactions: (1) 0.5 Ce2(g)+0.5Au2(g)=CeAu(g) (2) Ce2(g)+Au(g)=CeAu(g)+Ce(g) and (3) Ce2(g)=2 Ce(g), were found to be 24.7 ± 0.14,...
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Veröffentlicht in: | J. Chem. Phys. 54: 2621-6 (15 Mar 1971) 1971-01, Vol.54 (6), p.2621-2626 |
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Sprache: | eng |
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Zusammenfassung: | The Knudsen-cell mass spectrometric method has been used to study gaseous equilibria over the Au–Ce–CeS–BN–C system. The third-law enthalpies, ΔH0°, in kcal mole−1, of the reactions: (1) 0.5 Ce2(g)+0.5Au2(g)=CeAu(g) (2) Ce2(g)+Au(g)=CeAu(g)+Ce(g) and (3) Ce2(g)=2 Ce(g), were found to be 24.7 ± 0.14, 23.0 ± 0.16 and 58.0 ± 1.5, respectively. The corresponding second-law value for Reaction (3) is 53.4 ± 10. The reaction enthalpies for Reactions (1) and (2) were combined with the literature value for D0°(Au2) and the value of D0°(CeAu) obtained in the present investigation to yield the dissociation energy of diatomic cerium. The selected value for the dissociation energy of Ce2 is D0° = 57 ± 4 or D298° = 58 ± 4 kcal mol−1. Using the latter value and the literature value for the standard heat of sublimation of cerium, ΔHυ,298° = 101 ± 1 kcal mol−1, the standard heat of formation, ΔHf,298°, of diatomic cerium has been calculated as 144 ± 6 kcal mol−1. The stability of selected gaseous intermetallic cerium compounds has been predicted on the basis of the Pauling model of a polar bond and the experimental value for the dissociation energy of diatomic cerium. A reassessment of the dissociation energies, D0°, of LaAu, CeAu, PrAu, and NdAu [J. Chem. Phys. 52, 2956, (1970)] resulted in the values of 79.5 ± 5, 77.0 ± 3.5, 72.0 ± 5 and 70.6 ± 5 kcal mol−1, respectively. |
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ISSN: | 0021-9606 1089-7690 |
DOI: | 10.1063/1.1675222 |