We discussed an approximate analytical method of the description of emittance of a two-step electrode reaction based on the Taylor series expansion and a numerical method based on a Fourier series expansion. It was shown that time independence of the relaxation time of adsorption of the intermediate product corresponds to the fixed state. In such a case there is a possibility of deriving a dependence describing the emittance of a two-step electrode reaction. The accuracy of the derived formulae depends on the number of terms taken into account in the Taylor series expansion. For the transient state a time dependence is observed of the relaxation time of intermediate product adsorption. It is not possible to determine formulae describing emittance of a two-step electrode reaction in the intermediate state. It is impossible to solve this problem in the analytical form.