Nitrobenzene was adsorbed from saturated air at 33°C in cylinders of activated carbon 4 mm in diameter and 10 mm long. "The cylinders were embedded in Teflon with the top circular face exposed to the air so that only axial diffusion took place. The concentration profiles for nitrobenzene were measured at several times using nuclear magnetic resonance. Data taken at 64 bours are as follows: 

(a) Using 8 man as the penetration distance, calculate the average value of the effective diffusivity D_e,

(b) Using this value of D_e plot the predicted concentration profile and pare it with the measured profile. What might explain the difference?

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Distance, mm c/c. 2 0.78 4 0.48 0.11 8 0.01 10 0 alue