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Problem: The stagnant liquid B in a container that is 10 cm high (L = 10 cm) is exposed to the non-reactant gas A at time t = 0. The concentration of A, dissolved physically in B, reaches cA0  0.01mol/m3 at the interface instantly and remains constant. The diffusion coefficient of A in B is DAB  2109 m2/s. Determine the evolution of the concentration of A within the container. In the second part, repeat it but this time consider that A reacts with B according to the following reaction ABC rA 2107cA mol/[login to view URL] Method of Solution: The physical problem is sketched in the figure. The mole balance of A for the first part of the problem leads to c 2c ADA t AB z2 The boundary and initial conditions for above equation are: I.C. B.C.1 B.C.2 cA z,00 cA 0,t cA0 cA |zL 0 z forz0 for t  0 fort0 For the second part, moles of A are consumed by the liquid B while diffusing in it. Assuming that the concentration of the product C is negligible, so that the diffusion coefficient remains unchanged, the mole balance of A results in c 2c A D A kc tABz2 A Initial and boundary conditions remain the same as for the first part written above.