$3\mathrm{.}7.$ Countercurrent molecular diffusion of and in a tube. A tube, in inside diameter and $6$ inches long, has hydrogen blowing across one end and nitrogen across the other at $.($a$)$ For equimolar counter diffusion, what is the rate of transfer of hydrogen into nitrogen in mol$/$s$?$ Estimate the diffusivity from $(3-36)($b$)$ For part $($a$),$ plot the mole fraction of hydrogen against distance from the end of the tube past which nitrogen is blown.