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 ΔH_f298 values of $\text{−681.2±7}\mathrm{kcal}/\mathrm{mole}$ and $\text{−590.5±7}\mathrm{kcal}/\mathrm{mole}$ , 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 ΔH_f298 of $\text{35.1±4}\mathrm{kcal}/\mathrm{mole}$ and $\text{−56.3±4}\mathrm{kcal}/\mathrm{mole}$ for VO(g) and VO₂(g), respectively.