Effusion-Mass Spectrometric Determination of the Heats of Formation of the Gaseous Molecules V4O10, V4O8, VO2, and VO

Abstract

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.