THERMODYNAMICS OF THE ASSOCIATION REACTIONS OH- + H2O = HOHOH- AND CH3O- + CH3OH = CH3OHOCH3- IN THE GAS-PHASE

The temperature dependence of the equilibrium constants for the gas-phase reactions HO- + HOH = HOHOH- (1) and CH3O + HOCH3 = CH3OHOCH3- (2) was measured with a pulsed electron high-pressure mass spectrometer. The enthalpy ΔH° and entropy ΔS° changes were obtained from van't Hoff plots of the equilibrium constants. The enthalpy changes were found in good agreement with values reported by Meot-Ner and Sieck (-ΔH1° (kcal/mol):27.6, present work; 26.8, Meot-Ner. -ΔH2° (kcal/mol): 29.3, present work; 29.3, Meot-Ner). These values are also in good agreement with recent theoretical results. The agreement for the entropy changes is not as good (-ΔS1° (cal/(deg mol): 28.1, present work; 24.2, Meot-Ner. -ΔS2° (cal/(deg mol)): 31.8, present work; 27.6, Meot-Ner). Evaluations based on theoretical calculations predict -ΔS1° = 24.6 and -ΔS2° ≈ 27.9 cal/(deg mol). © 1990 American Chemical Society.