This paper presents a numerical analysis of the chemical-electrochemical (CE) mechanism of a rotating disk electrode at steady-state. Two sets of kinetic constants (denominated "fast kinetics" and "slow kinetics") were used to evaluate how they alter the original concentration profiles and the current response. Comparing the results obtained with those in the literature allows concluding that the range of validity of the reaction layer hypothesis, although able to accurately predict the current density in some cases, is intrinsically limited, because it will always fail for sufficiently high rotation speeds. Hence, a system with "fast kinetics" is merely one in which the hypothesis is applicable for all the rotation speeds that were studied. It was also observed that the range of validity of the reaction layer hypothesis is independent of the equilibrium constant of the chemical process and is determined solely by the absolute values of the kinetic constants. (C) The Author(s) 2018. Published by ECS.