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  • The irreversible, first-order reaction of gaseous A → B occurs in spherical catalyst pellets with a radius of 2 mm. For this problem, the molecular diffusivity of A is 1.2 X 10 −1 cm 2 /s and the Knudsen diffusivity is 9 X 10 −3 cm 2 /s. The intrinsic first-order rate constant determined from detailed laboratory measurements was found to be 5.0 s −1 . The concentration of A in the surrounding gas is 0.0 I mol/L. Assume the porosity and the tortuosity of the pellets are 0.5 and 4, respectively. Determine the Thiele modulus for the catalyst pellets. Find a value for the internal effectiveness factor. For an external mass- transfer coefficient of 32 s-I (based on the external area of the pellets), determine the concentration of A at the surface of the catalyst pellets.
  •  (d) Find a value for the overall effectiveness factor.