Activity coefficients and thermodynamics of hydrobromic acid in methanol-water mixtures and anhydrous methanol from electromotive force studies

Abstract

two reactions a selected value of Dm*(CaF) = 127.5 ± 2.5 kcal. mole-1 appears to be appropriate.The thermodynamic consistency of this value can be tested by considering the following reactions. For example, Reactions 3 and 4 may be combined to give Reaction 2 and indicate a value of D»9s(CaF) = 126 ± 3 kcal. mole ', in good agreement with the result of Reactions 1 and 2. Reactions 5, 6, and 7 lead to identical enthalpies of formation for BeF, and one can infer that the value of Dh«(CaF) equal to 127.5 kcal. mole-1 is at least as reliable as, and self-consistent with, the AH°( BeF,) and 7)298 (A1F) values.From the Ds9«(CaF) value of 127.5 kcal. mole-1 and the enthalpy of Reaction 8 one obtains a77°98 (SiF») = 288.7 ± 6 kcal. mole-1, whereas Reaction 9, which is independent of flS* (CaF), implies A77"98 atoms (SiF,) = 288 ± 2 kcal. mole-1. Thus, these reactions are also consistent with a value of D|w(CaF) = 127.5 kcal. mole-1.By taking the value of / ,96 at()ms SiF» equal to 288 ± 2, as indicated by Reactions 8 and 9, Reactions 10 to 12 yield the following self-consistent values: Dhs(CaF) = 127.5 ± 2.5, 70»98(SiF) = 136 ± 4 (Reactions 10 and 12) or 134 ± 2 (Reaction 13), D°%(GeF) = 119.8 ziz 3 (Reaction 11), or 126 ziz 5 (Reaction 10), all in kilocalories per mole. Hence the CaF dissociation energy is further verified. From Reaction 14 and the known enthalpies of formation, [aTíTikIScF.O = -383.9 kcal. mole-1] (11) and vaporization (8, 12), one calculates D°98 (CaF) = 122 zb 8 kcal. mole-1.