2. A solid reactant B is a form of large disk with the thickness of 2L, where its radius is assumed to be very larger than the thickness (R >

L). As soon as this reactant is fully exposed to a gas reactant A with the initial concentration of CA0, the following reactionprogresses: \mathrm{A}(g)+b \mathrm{~B}(s) \rightarrow \mathrm{P}(g)+\mathrm{S}(s), \text { where } g=\text { gas and } s=\text { solid } The product S is a kind of solid ash and the rate constant is greatly high at the interfacebetween the reactant A and product S. A) When the diffusion across the ash layer of the product S is rate determining, express the overall reaction rate equation as a function of CA0- [2 point] B)Derive the relationship between the reaction time (t) and the conversion of B (XB) on the basis of your solution in Problem A. [2 point]