EXAMPLE PROBLEM: Molecular Diffusion of Helium in Nitrogen

A mixture of He and $N_2$ gas is contained in a pipe at $298K$ and $1$atm total pressure which is constant throughout.At one end of the pipe at point $1$ the partial pressure $P_{A1}$ of $He$ is $0\mathrm{.}60$atm and at the other end $0\mathrm{.}2m(20cm)P_{A2}=0\mathrm{.}20$ atm. Calculate the flux of He at steady state if $D_{AB}$ of the $He-N_2$ mixture is $0\mathrm{.}687{10}^{-4}\frac{m^2}{s}(0\mathrm{.}687c\frac{m^2}{s}).$ Use SI and cgs units.