Comment on the possible role of the reaction H~·*+H2O→H2+~·OH in the radiolysis of water at high temperatures

摘要

In a recent paper (Radiation Physics and Chemistry, 2005, vol. 74, pp. 210) it was suggested that the anomalous increase of molecular hydrogen radiolysis yields observed in high-temperature water is explained by a high activation energy for the reaction H~·+H2O→H2+~·OH. In this comment we present thermodynamic arguments to demonstrate that this reaction cannot be as fast as suggested. A best estimate for the rate constant is 2.2 x 10~3 M~(-1) s~(-1) at 300 °C Central to this argument is an estimate of the OH radical hydration free energy vs. temperature, ΔG_(hyd)(OH) = 0.0278t-18.4kJ/mole (t in °C, equidensity standard states), which is based on analogy with the hydration free energy of water and of hydrogen peroxide.