Consider a system in which gas A diffuses through a stagnant film through the surface of a non porous catalyst particle where it reacts irreversibly according to nAk1B . Obtain the flux at the surface when the reaction is very fast and instantaneous. Notice that it the reaction is very fast A will be consumed instantly. And the surface BC will be that xA=0 at the surface r=R. and xA=xA0 at r=r.