Following the comment article by Koppenol (W. H. Koppenol, Phys. Chem. Chem. Phys., 2021, 23, DOI: 10.1039/D1CP03545B), the H2O2 decomposition reaction mechanism based on the production of a de facto monovalent iron ion hydration complex, which is theoretically proposed in T. Tsuneda and T. Taketsugu, Phys. Chem. Chem. Phys., 2018, 20, 24992-24999, is reviewed from the standpoint of chemical kinetics. As a result, it is found that this decomposition mechanism is strongly supported by comparing the Gibbs energies of formation in consideration of the O-O bond dissociation of H2O2 for de facto monovalent iron, ferrous, and ferric ion complexes.