In this work, we analyze the influence of interfacial reaction and adsorption processes over the predictions of the unsteady average macroscopic concentrations in slurries. The isothermal mass transport model consists of the equations for the well-mixed fluid and the one corresponding to the pellets. The latter consist of porous media where first-order reaction kinetics and linear adsorption take place. The interfacial flux boundary condition considers the mass transfer resistance in the fluid, as well as superficial reaction and accumulation terms. The model solution is carried out by means of Fourier series expansions. It is shown that, unless the adsorption and reaction at the surface of the porous pellets are much more intense than in the bulk, the error introduced by not considering these interfacial phenomena is negligible. The results from this work are relevant for improving design and control applications of slurries involving fast reactions or strong adsorption.