The reduction of oxygen and hydrogen peroxide on the Au(100) surface has been studied using classical electroanalytic methods combined with in situ X-ray scattering techniques in order to relate surface structure to the kinetics. Confirming previous results, the 4e(-) reduction pathway for O-2 at low overpotentials gives way to a 2e(-) path at higher overpotentials. It was determined that, contrary to previous speculation, the (1x1) --> "hex" reconstruction transition is not the dominant mechanism for this change in reaction pathway since the transition in reduction kinetics occurs in a much narrower potential range than the (1x1) --> "hex" transition. The time constants for the two transitions differ by approximately 2 orders of magnitude, with the structural transition the slower. We suggest that the change in reaction pathway is related to the potential dependence of the adsorption of hydroxyl anions that catalyze the reduction of peroxide.