A mathematical model for the steady state of an isothermal two-phase continuous stirred tank reactor has been developed. It consists of a lumped model for the liquid phase and a distributed model for the solid phase. Interphase mass transfer is simulated using the film model. Non-catalytic reaction takes place in the solid particles only and, in general, the overall rate of reaction is dominated by mass transfer phenomena. Discretization of both residence time and diameter of the solid particles is done in order to solve the problem numerically, and an iterative procedure is suggested for the solution of the model. Simulation results were obtained and the effect of variations in the residence time, equilibrium constant, porosity of the original particle and mean particle diameter is discussed.