The theory of adsorption pseudocapacity behavior is developed for a sequence of electrochemical reactions involving an ion discharge step which produces an adsorbed radical, followed by a n "ion-atom" recombination reaction with or without desorption of the product of this step. The adsorption pseudocapacity behavior is deduced analytically particularly for the steadystate case and distinguished from the results obtained for assumed quasi-equilibrium in the ion discharge step when the succeeding step is rate-controlling. The effect of variation of the relative values of the rate constants of the discharge and of succeeding steps is investigated. I t is shown that the capacity-potential behavior is sensitively dependent 011 the ratio of these rate constants, particularly for the case of adsorption isotherms involving a large value for the "heterogeneity parameter", r , defining the variation of energy of adsorption of the intermediates with coverage. Under the latter conditions, limiting coverages of the electrode by the adsorbed species are reached with increasing potential, depending on the relative valiles of the rate constants and the value of r.Alost electrochemical reactions not involving simple metal-ion redox reactions proceed by two or more consecutive steps. Under these circumstances, adsorbed inter~nediates are involved, the surface concentrations of which are usually potential dependent. Since Faradaic charge is involved in the formation of the layer of intermediates, the potential dependence of the coverage leads to an adsorption pseudocapacitance (1, 2).2 The importance of studies of charging curves was already recognized by Bowden and Rideal(3) with regard to the ionic double-layer and the method was developed by Slygin and Frumlrin (4-6) for the study of H atom adsorption in the hydrogen evolution reaction; a t about the same time, Butler and Drever (7) used this method for the study of oxide films and Pearson and Butler ( 8 ) examined electrochemical hydrogen adsorption a t the platinum metals by means of charging curves. Studies of charging curves and the corresponding adsorption pseudocapacitance can provide an important method, complementary to direct kinetic current-potential studies, for elucidation of electrode reaction mechanisms. 3Iuch contemporary interest in electrochemical kinetics centers around the study of charging curves and the measurement of electrode capacitance, but further work is required in the interpretation of such data.In a previously published paper (9), we have shown how studies of the dependence of adsorption pseudocapacitance upon potential can lead to information on the type of isotherm governing the adsorption of reaction intermediates, and to information about the potential dependence of coverage by such intermediates in two or multistep electrochelnical reactions. In another paper (lo), we have shown how these theoretical considerations can be applied to the elucidation of the adsorption behavior of intermediates involved in electrochemical decarboxj~lation react...