4.9 An old-fashioned glass apothecary jar contains a patent medicine. The neck is closed with a rubber stopper that is 20mm tall, with a diameter of 10mm at the bottom end, widening to 20mm at the top end. The molar concentration of medicine vapor in the stopper is 2103kmol/m3 at the bottom surface and is negligible at the top surface. If the mass diffusivity of medicine vapor in rubber is 0.2109m2/s, find the rate (kmol/s) at which vapor exits through the stopper