A. A reactant A diffuses to a surface, at which a reaction occurs according to the following stoichiometry: A(g) → B(g) + C(g). Under what conditions can we ignore the convective flux of A? a. We cannot, because 2 moles of product gas (B+C) diffuse away from the surface for every 1 mole of reactant (4) that diffuses to the surface. b. If the medium above the surface is quiescent and the concentration of A is dilute throughout the medium. c. If the medium above the surface is quiescent and the concentration of both B and C are dilute throughout the medium. B. Why does convection not occur at a solid boundary? a. No slip in normal direction and no penetration in the tangential direction. b. No slip in tangential direction and no penetration in the normal direction. c. Because the reactant becomes trapped in the pores of the surface and cannot pass through. d. Both (b) and (c) are correct.