This Demonstration plots the dimensionless concentration, , versus time for user-set values of the reactor's residence time, catalyst deactivation, and first-order reaction rate constants. Here the feed concentration of species to the reactor and its initial concentration in the reactor are both taken equal to . You can observe the behavior of catalyst activity versus time, which depends solely on the catalyst deactivation rate constant. It is found that the dimensionless concentration, , goes through a minimum when there is deactivation; it reaches a steady state value when (the case of no deactivation) as displayed in the second snapshot.