Heterogeneous Reactions Studied by Mass Spectrometry. II. Reaction of Li2O(s) with H2O(g)

The reaction of water vapor with lithium oxide was studied by a mass‐spectrometric technique. In the temperature range 1100–1400°K and with water vapor pressures of the order of 0.1 mm, the major reaction product in the vapor phase was LiOH. Smaller amounts of Li₂(OH)₂ and traces of Li₃(OH)₃ were measured. Various equilibria among the above species were studied with the use of isotopic substitution for lithium and hydrogen. The decomposition of lithium hydroxide was studied in the temperature range 500–600°K. Structural parameters and vibrational frequencies were estimated and thermodynamic functions were calculated for the LiOH and Li₂(OH)₂ molecules. The following heats of reaction, which are consistent within experimental error, were then determined: $$\begin{array}{cc}{\mathrm{Li}}_2\mathrm{O}(\mathrm{s}\mathrm{)+}{\mathrm{H}}_2\mathrm{O}(\mathrm{g}\text{)→2}\mathrm{LiOH}(\mathrm{g})& {\mathrm{\Delta H}}_{1300}^{\circ }\text{=79.0±2.0\hspace{0.17em}}\mathrm{kcal}\\ {\mathrm{Li}}_2\mathrm{O}(\mathrm{s}\mathrm{)+}{\mathrm{H}}_2\mathrm{O}(\mathrm{g}\mathrm{)\to }{\mathrm{Li}}_2(\mathrm{OH}{)}_2(\mathrm{g})& {\mathrm{\Delta H}}_{1250}^{\circ }\text{=15.0±2.0\hspace{0.17em}}\mathrm{kcal}\\ {\mathrm{Li}}_2(\mathrm{OH}{)}_2(\mathrm{g}\text{)→2}\mathrm{LiOH}(\mathrm{g})& {\mathrm{\Delta H}}_{1300}^{\circ }\text{=60.0±3.0\hspace{0.17em}}\mathrm{kcal}\\ 2\mathrm{LiOH}(\mathrm{s}\mathrm{)\to }{\mathrm{Li}}_2\mathrm{O}(\mathrm{s}\mathrm{)+}{\mathrm{H}}_2\mathrm{O}(\mathrm{g})& {\mathrm{\Delta H}}_{500}^{\circ }\text{=30.4±1.0\hspace{0.17em}}\mathrm{kcal}\\ 2\mathrm{LiOH}(\mathrm{s}\mathrm{)\to }{\mathrm{Li}}_2(\mathrm{OH}{)}_2(\mathrm{g})& {\mathrm{\Delta H}}_{600}^{\circ }\text{=45.0±3.0\hspace{0.17em}}\mathrm{kcal}.\end{array}$$