Consider a long porous catalyst cylinder. because of the arrangement of the pores the concentration gradient of reactant a is c_a = c_as(r/r)^2. what is the total amount of a reacting, mol/s, in any 1 cm length of the cylinder if the radius is 3 cm, the effective diffusivity, d_eff, is 10^-3 cm^2/s, and the concentration at the external surface is 0.001 mol/cm^3. note you can neglect end effects and the concentration is only going to depend on radius.