Thermochemistry of the Gaseous Vanadium Chlorides VCl, VCl2, VCl3, and VCl4


J. Phys. Chem. A 2008, 112, 40, 9978–9982 Publication Date:September 6, 2008


Gaseous equilibria in the V−Ag−Cl system were studied at elevated temperatures by effusion-beam mass spectrometry, where the pertinent species were generated by reaction of Cl2(g) with V + Ag granules in the effusion cell source. Reaction enthalpies were derived from the equilibrium data, and the standard enthalpies of formation at 298 K of gaseous VCl, VCl2, and VCl3 were found to be +49.7, −34.8, and −85.6 kcal mol−1, respectively. The corresponding bond dissociation energies at 298 K are D(V−Cl) = 102.9 kcal, D(ClV−Cl) = 113.5 kcal, D(Cl2V−Cl) = 79.8 kcal, and D(Cl3V−Cl) = 69.5 kcal. From these data, the dissociation energy D°0(VCl) = 101.9 kcal mol−1 or 4.42 eV is obtained. An alternate value, ΔfH°298(VCl3,g) = −87.0 kcal mol−1 was derived from third-law analysis of literature sublimation data for VCl3(s). In addition, literature thermochemical data on VCl4(g) were re-evaluated, leading to ΔfH°298 = −126.1 kcal mol−1. The results are compared with various estimates in the literature.

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