Chapter 14, Problem 14.9P

An old-fashioned glass apothecary jar contains a patent medicine. The neck is closed with a rubber stopper that is 20 mm tall, with a diameter of 10 mm at the bottom end, widening to 20 mm at the top end. The molar concentration of medicine vapor in the stopper is $2\times {10}^{-3}$ ${\text{kmol/m}}^{\text{3}}$ at the bottom surface and is negligible at the top surface, lf the mass diffusivity of medicine vapor in rubber is $2\times {10}^{-9}$ $m^2/s$ . find the rate $\left(kmol/s\right)$ at which vapor exits through the stopper.