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Temperature Dependence of the Acid Dissociation Constant of the Hydroxyl Radical



G A. Poskrebyshev, Pedatsur Neta, Robert E. Huie


The acid dissociation constant of the hydroxyl radical in aqueous solution was determined by pulse radiolysis from the pH dependence of the rate constant for reaction of the OH/O - radical with benzoate ions. The rate constant and the pKa( OH) values were determined over the temperature range 284 K to 343 K. At 298 K, pKa298( OH) = 11.57 0.04 and DionGo298( OH) = (66.4 0.2) kJ mol-1. From the temperature dependence of Ka( OH) we calculate DionHo298( OH) = (24.4 0.5) kJ mol-1 and DionSo298( OH) = (-141 2) J mol-1 K-1. These values lead to the heat of formation DfHo298(O -) = (17.3 to 20.2) kJ mol-1 and So298(O -) = -45 J mol-1 K-1 for O -. The activation energy for the reaction of OH with C6H5CO2- was found to be (8.8 0.6) kJ mol-1 and the Arrhenius pre-exponential factor (2.4 0.6) 1011 L mol-1 s-1.
Journal of Physical Chemistry A
No. 47


acid dissociation constant, equilibrium constant, hydroxyl radical, ionization


Poskrebyshev, G. , Neta, P. and Huie, R. (2002), Temperature Dependence of the Acid Dissociation Constant of the Hydroxyl Radical, Journal of Physical Chemistry A (Accessed July 22, 2024)


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Created October 31, 2002, Updated October 12, 2021