Consider a first order reaction taking place on the surface of a catalyst with cylindrical pores The relevant equation is with the following boundary conditions at at Here is the pore length and is the surface concentration of species The second boundary condition specifies that there is no flux of material through the interior end of the cylindrical catalyst pores The concentration of reactant within a pore is given by where is the Thiele modulus and This Demonstration plots the dimensionless concentration versus the dimensionless distance within the pores for userset values of the Thiele modulus It also gives the value of the effectiveness factor where is the average concentration of species in the catalyst pores