Effusion-mass spectrometric determination of the heats of formation of the gaseous molecules V4O10, V4O8, VO2, and VO

An effusion-mass spectrometric investigation of the vapor in equilibrium with the vanadium compounds, V2O5, V2O4, and V2O3, was conducted. The only congruently evaporating solid was V2O3, while the others decomposed to various vapors and V2O3 in the temperature range 1000–1200°K. The vapor over V2O5 was found to contain the compounds V4O10(g) and V4O8(g) with resulting ΔHf298 values of −681.2±7 kcal/mole and −590.5±7 kcal/mole, respectively. A study showed that the vapor over V2O3 at 2270°K contained the species V(g), VO(g), and VO2(g), yielding values for ΔHf298 of 35.1±4 kcal/mole and −56.3±4 kcal/mole for VO(g) and VO2(g), respectively.