Diffusive Fluxes and Concentration Changes

Consider the concentration pro!le C$($x$)=$ Coe$$ax along the positive x$-$axis $(0\text{'}$ x

$<$ $$),$ where Co and a are constant positive parameters. $($a$)$ Calculate the size and

direction of the diffusive $"$ux as a function of x produced by the constant diffusivity D$.$

$($b$)$ Calculate the corresponding in situ concentration change, $-$C$/-$t$,$ due to diffusion.

Numbers: Co $=1$ mmol L$1$

a $=0\mathrm{.}02$ m$1$

D $=1\backslash$times $109$ m$2$ s$1$

Evaluate $"$ux F and concentration change, $-$C$/-$t$,$ at x $=0,10$ m$,100$ m$,1$ km$.$