The flowing afterglow measurements of the equilibrium constants for selected proton transfer reactions have been extended to temperatures other than room temperature in order to completely specify the thermodynamics of such reactions. The van't Hoff analysis of the data for the reaction CO2H++CH4CH5++CO2 results in a value for the standard enthalpy change, ΔH° (196 to 553°K), of −0.064±0.004 eV and for the standard entropy change, ΔS° (196 to 553°K), of +1.4±0.6 e.u. Studies of the reaction N2OH++COCOH++N2O led to a value of −0.151±0.009 eV for ΔH° (277 to 505°K) and a value of −1.8±1.1 e.u. for ΔS° (277 to 505°K). ΔH° is a direct measure of the difference between the proton affinities of CO2 and CH4 in the former case and of N2O and CO in the latter. The measured values for ΔS° yield differences in the standard entropies of the protonated species: S̄°298(CH5+)−S̄°298(CO2H+)= −5.2± 0.6 e.u and S̄°298(COH+)−S̄°298(N2OH+)= −7.1± 1.1 e.u. Reference to calculated values for the standard entropy of CH5+ and COH+ yields values for the standard entropy of CO2H+ and N2OH+ and some indication of the structure of these species.

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