Q$3.$ Olson and Smith $(1950)$ measured the rates of oxidation of $S{O}_2$ with air in a differential, fixed$-$bed reactor. The platinum catalyst was deposited only in the outer surface of the $0\mathrm{.}3-cm0\mathrm{.}3-cm$ cylindrical $A{l}_2{O}_3$ pellets so that intraparticle transport effects were negligible. Bulk gas compositions entering and leaving the reactor and flow rate were measured. Hence, the global rate could be calculated from the equation for differential reactors: $(-r_A)=\frac{F(x)}{W}.$ Calculate the magnitude of $C_b-C_s.$ Experimental global rates are given thus for two levels of conversion of $S{O}_2$ to $S{O}_3.$

$\backslash$table$[[$Mean conversion of $S{O}_2,r_p,$kgmolS$\frac{O_2}{\text{k}\text{g}\text{c}\text{a}\text{t}\text{s}},p_b,Pa$