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The kinetics of decomposition of H2O2 catalyzed by Fe3+ in aqueous solution in the presence of HNO3 has been followed by permanganate titration and studied by the initial-rate method. In the experimental range H2O20/Fe3+ = 41−2028 used in this study, the initial rate follows the law v0 = k (Fe3+3/2H2O201/2) / (H+3/2) / (1 + k' (Fe3+/ (H2O20H+) ) ) 1/2. Both rate constants k and k' decrease with increasing ionic strength, and the corresponding apparent activation energies are 146 ± 10 and 88 ± 21 kJ mol-1. The experimental rate law strongly suggests a radical-chain mechanism, with Fe2+, HO•, HO2•, and O2•- as propagating intermediates. At high values of the H2O20/Fe3+ ratio two different reactions compete as chain-termination steps (dismutation of HO2• radicals and reduction of HO2• by Fe2+), whereas at lower values of that ratio a third chain-termination step (reduction of HO• by Fe2+) also contributes. Thus, the kinetics of this reaction can be considered as an indirect proof of the participation of hydroxyl radicals in the mechanism.
Joaquin F. Perez‐Benito (Fri,) studied this question.