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Radiation Physics and Chemistry
Year: 2009  |  Volume: 78  |  Issue: 3  |  Page No.: 191 - 194

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

David M. Bartels    

Abstract: 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 2.2×103 M−1 s−1 at 300 °C. Central to this argument is an estimate of the OH radical hydration free energy vs. temperature, ΔGhyd(OH)=0.0278t−18.4 kJ/mole (t in °C, equidensity standard states), which is based on analogy with the hydration free energy of water and of hydrogen peroxide.

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