Q$1.$ A very thick slab has a uniform concentration of solute $A$ of $c_0=1\mathrm{.}0{10}^{-2}$kmol$\frac{A}{m^3}.$

Suddenly, the front face of the slab is exposed to a flowing fluid having a concentration $c_l=0\mathrm{.}20$

kmol$\frac{A}{m^3}$ and a convection coefficient $k_c=2{10}^{-7}\frac{m}{s}.$ The equilibrium distribution coefficient

for this system is $K=\frac{c_{Li}}{c_i}=2\mathrm{.}0.$ The diffusivity in the solid is $D_{AB}=4{10}^{-9}\frac{m^2}{s}.$ Assuming

that the slab is a semi$-$infinite solid, calculate the concentration in the solid at the surface, and at

$(x=0\mathrm{.}01m)$ from the surface after $t=3{10}^{4}s.$ Also, comment on the direction of the diffusion.