  We present a study exploring the range of applicability of a generalized Fick
Jacobs equation in the case when diffusive mass transport of a fluid along a
pore includes chemical reactions in the bulk and pore surface. The study
contemplates nonequilibrium boundary conditions and makes emphasis on the
comparison between the predictions coming from the projected Fick Jacobs
description and the corresponding predictions of the original two dimensional
mass balance equation, establishing a simple cuantitative criterion of validity
of the projected description. For the adsorption desorption process, we
demonstrate that the length and the local curvature of the pore are the
relevant geometric quantities for its description, allowing for giving very
precise predictions of the mass concentration along the pore. Some schematic
cases involving adsorption and chemical reaction are used to quantify with
detail the concentration profiles in transient and stationary states involving
equilibrium and nonequilibrium situations. Our approach provides novel and
important insights in the study of diffusion and adsorption in confined
geometries.
