Component A diffuses from a wall at concentration $C_{A_0}$ as shown in the following

figure. The concentration of component $A$ at $z=$ is $C_A.$

$($a$)$ What is the "film theory"?

$(7\%)$

$($b$)$ Use the concept of film theory, find the concentration of component A in one

dimension mass transfer. $,(10\%)$

$($c$)$ Find the relation between $k_e$ and $D_{NB},$ where $k_e$ is the convective mass transfer

coefficient.