Reactant A diffuses and reacts within a spherical, porous catalyst. The reaction is first-order and irreversible. At zero time, the catalyst, which contains no A, is dropped into a liquid bath containing a constant concentration of A. Use a shell balance to derive the governing partial differential for the concentration c(r, t) of A within the catalyst. Also, specify the initial and boundary conditions, assuming that the mass-transfer Biot number1 is infinite