The study of electrochemical processes preceded by a homogeneous chemical reaction has been extensively tackled in electrochemistry due to the fact that these embrace many real systems of relevance in several scientific fields. The literature abounds with approaches to these systems, most of which assume simplifying hypotheses such as the well-known kinetic steady state approximation, even in planar diffusion. In this paper we present a rigorous analytical solution for CE mechanism in Normal Pulse Voltammetry valid for spherical electrodes of any size, as a series of two dimensionless variables, one related to the chemical kinetics and the other to the electrode sphericity. The rigorous solution has shown an excellent convergence and has permitted us to study, without any limitation, the CE mechanism response and the influence of kinetic rate constants, equilibrium constant, electrode sphericity and initial presence of electrode product. Furthermore, it has been possible to establish the validity of kinetic steady state approximated solution. indicating that this involves significant errors for small values of electrode sphericity, kinetic rate constants and equilibrium constant. (C) 2009 Elsevier B.V. All rights reserved