Mass-Spectrometric Study of the Reaction of Water Vapor with Solid Barium Oxide

Barium oxide disks in a platinum Knudsen cell were reacted with water vapor at temperatures between 1485° and 1785°K and water pressures up to approximately 10^—4 atm. The effusing molecules were identified and measured mass‐spectrometrically. Although no Ba(OH)₂⁺ ion was observed, the species BaOH⁺ was inferred to have come from both BaOH and Ba(OH)₂ because of its dependence on the water pressure. From the observed equilibria, $$\begin{array}{cc}\mathrm{BaO}(\mathrm{s}\mathrm{)+}{\mathrm{H}}_2\mathrm{O}(\mathrm{g}\mathrm{)\to }\mathrm{Ba}(\mathrm{OH}{)}_2(\mathrm{g})& {\mathrm{\Delta H}}_0^{\circ }\text{+\hspace{0.17em}50.0\hspace{0.17em}}\mathrm{kcal}/\mathrm{mole},\\ \mathrm{BaO}(\mathrm{s}\mathrm{)+}\mathrm{BaO}(\mathrm{g}\mathrm{)+}{\mathrm{H}}_2\mathrm{O}(\mathrm{g}\text{)→2}\mathrm{BaOH}(\mathrm{g}\mathrm{)+}\frac{1}{2}{\mathrm{O}}_2(\mathrm{g})& {\mathrm{\Delta H}}_0^{\circ }\text{=122.3\hspace{0.17em}}\mathrm{kcal}/\mathrm{mole},\\ 2\mathrm{BaO}(\mathrm{g}\mathrm{)+}{\mathrm{H}}_2\mathrm{O}(\mathrm{g}\text{)→2}\mathrm{BaOH}(\mathrm{g}\mathrm{)+}\mathrm{O}(\mathrm{g})& {\mathrm{\Delta H}}_0^{\circ }\text{=\hspace{0.17em}69.2\hspace{0.17em}}\mathrm{kcal}/\mathrm{mole}.\end{array}$$ These lead to a HOBa–OH bond energy of 99 kcal/mole and a Ba–OH bond energy of 107 kcal/mole. The latter number differs significantly from a value deduced from studies of flame spectra and implies that the concentration of hydroxide species in these flames has been underestimated by several orders of magnitude.