Helium gas is seperated from other components of a gas mixture by its selective diffusion through the wall of a Pyrex glass tube. Under steady-state conditions, the partial pressures of helium at the inner and outer surfaces of the Pyrex tube are 1.5 and 1.0 bar, respectively. If the wall thickness of the Pyrex tubing is 3 mm, determine a. the flux of He through a tube having an inside diameter of 1.0 cm; b. the concentration profile, cA(r), of helium within the wall.