Transient Diffusion in a Porous Medium with Reversible Adsorption Assume that species A is able to diffuse within some porous material, where it is reversibly adsorbed on the solid phase. Let S denote the adsorbed form of A. The rate of adsorption is given by Rvs=kACAksCs Where the concentrations CA and CS are based on total volume (fluid plus solid). With the prous material modeled as a homogeneous medium, the effective diffusivity of A is DA. The adsorbed species is assumed to be immobile, so that DS=0. The porous medium, which occupies the space x>0, initially contains no A or S. Starting at t=0,CA=C0 at x=0. Use an order of magnitude analysis to show that for short contact times, the concentration profile for A is approximately the same as if there were no adsorption. Suitable dimensionless variables are =C0CA,=KC0CS,=tkA,X=x(DAkA)21 where K=kSkA