20.3-1. Numerical Method for Unsteady-State Diffusion. A solid slab 0.01 m thick has an initial uniform concentration of solute A of 1.00 kg mol/m. The diffusivity of A in the solid is DAB = 1.0 x 10-10 m/s. All surfaces of the slab are insulated except the top surface. The surface concentration is suddenly dropped to zero concentration and held there. Unsteady-state diffusion occurs in the one x direction with the rear surface insulated. Using a numerical method, determine the concentrations after 12 x 104 s. Jse Ax = 0.002 m and M = 2.0. The value of K is 1.0. G = 0 (front surface, r=0 m) C2 = 0.3125 kg mol/m (x=0.002 m) Cz=0.5859 (x = 0,004 m hAns. Co = 0.7813 (x = 0.006 m =0.8984 (X= 0.008 m co=0.9375 insulated surface, x = 0.01 m