Q3 (a) The following mechanism shows the formation of ethylene from acetylene by using Ni catalyst, where S represent the surface site. (1) C2H2 + S = C2H2-S (2) C2H2-S + H2 + C2H4 Determine the Eley-Rideal rate expression for the reaction if reaction in step (2) is the rate determining step. (8 marks) (b) If the rate determining step in Q3(a) is a reversible reaction as below, determine the Eley-Rideal rate expression for the reaction. Denote k as forward rate constant and k' as reverse rate constant. (1) C2H2-S + H2 = C2H4-S (2) C2H4-S C2H4 + S (12 marks)