Question 2: Diffusion plus convection with chemical reaction Pure gas A diffuses from the bulk gas (point 1) to a catalyst surface (point 2) where it irreversibly reacts to produce gas B. The balanced chemical reaction is given as: 4A(g) 3B(g) Once formed, the gas B diffues back a distance S to point 1. (a) Derive the equation (or expression) that should be used to calculate the molar flux of A, NA, in terms of the constant total concentration, c, the diffusivity, DAB, the distance, d, and the mole fractions of component A, XA2 and XA1. [7 Marks] = (b) If the reaction takes place instantaneously, and if the distance from point 1 to point 2 is 8 = 3 mm, the diffusivity of gas A in B is DAB = 5 x 10 m/s, the partial pressure of gas A at point 1 is pai = 101.325 kPa, and the system is at a total pressure of P = 101.325 kPa and a temperature of T = 300 K, calculate the molar flux of gas A, NA- Take R = 8.314 J/molk [3 Marks] =