Estimation of rate constants as a function of temperature for the reactions W + XYZ = WX + YZ, where W, X, Y, and Z are H or O atoms

Rate constants have been estimated as a function of temperature for seven reactions of the type W + XYZ = WX + YZ, where W, X, Y, and Z are H and O atoms. From transition state theory and estimates of the heat capacities of activation,\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm int\, k/[cm}^{\rm 3} {\rm (mol} \cdot {\rm sec)] = 10}^{{\rm 15}{\rm .87}} \exp (\Delta S_{298}^{\circ _ \ne} /R)T^{0.75} \exp [- (\Delta H_{298}^{\circ _ \ne} + 0.74)/RT] $$\end{document}where int k is the rate constant per transferable atom for the forward and reverse reactions in the exothermic direction, and where Δ H ° ≠298 is in kcal/mol. Values of Δ S ° ≠298 and Δ H ° ≠298 were obtained from the above equation and previously measured and evaluated rate constants at 298°K. The results are summarized in a table. Rate constants were calculated at temperature from 250 to 2000 K. The estimated rate constants were compared with recommended values. The results for Δ H ° ≠298 for reactions (15), (16), (17), and (19), in which a stable intermediate may precede the transition state, together with similar results previously found for reactions X + YZ = XY + Z, suggests that many such reactions may have values of Δ H ° ≠298 that are close to zero. The result for the reaction O + O 3 = O 2 + O 2 is however, an exception to the foregoing perhaps because it is the reaction of a singlet with a triplet.Δ S ° ≠298 for the same reaction is unexpectedly low.