The isothermal CSTR operates in steady state to carry out the liquid phase reversible reaction A to B. B is absent from the input stream, and the concentration of A there is 20 mol/lit. At residence lengths of 4 s and 8s, the concentrations of A at the reactor exit are 10 mol/lit and 5 mol/lit, respectively. Suppose that the first order rate law applies to the forward and backward reactions. Assume as well that the molar density of the system is constant. Get the forward reaction's rate constant (in s1)