Liquid-phase mass transfer in ion exchange controlled by diffusion across a Nernst film was studied. The expression for the momentary ion fluxes in systems without chemical reactions which was derived in a previous article is expanded to the more general case of systems where an irreversible chemical reaction occurs inside the film. In the case of two counterions and two colons an analytical solution is obtained, which for the first time allows arbitrary valences to be adopted for all ions. For the general case of any number of counterions and colons the original system of differential equations is reduced to a set of nonlinear, algebraic equations, which are much easier to solve. Exemplary calculations show that the introduction of an irreversible chemical reaction does not necessarily increase the effective diffusion coefficients of the ions and that in systems with chemical reactions in the film the total concentration at the resin boundary may substantially differ from that in the bulk, even for small fractions of the reacting colons.