Question

k1f M Br2 Br Br M kir (1) + k2,f BrH2 HBr H k2,r (2) + + ka,f HBr Br HBr2 (3) + + Experimentally measured rate expression for [HBr] given as below: d [HBr] Aexp [H2] [Br2]1/2 [HBr] 1+ A2expBr2 dt Consider the above elementary reactions mechanism proposed by Bodenstein to explain their experimental findings of the reaction rate of HBr. Reactions 1 and 2 are bi-directional (forward and reverse) while reaction 3 is uni-directional (forward only) as written. Bodenstein has been able to experimentally measure A1exp and A2exp. Please refer to formula sheet for chemical kinetics relationships if needed A2.1 Write the rate expression for the formation of the radicals (H and Br), as well as the reactants (H2 and Bra) product (HBr) using your knowledge of the chemical kinetics for elementary reactions. (5 marks) A2.2 Assuming that the radicals are in steady state, simplify the expression written by you in A2.1 for rate of formation of HBr, and hence relate A1exp and A2.exp to the rate constants from the elementary reactions above (that is, kif, ktr etc). (10 marks) A2.3 Comment on what this overall reaction rate implies with regards to the influence of the concentration of HBr on the reaction rate (will it increase or decrease if [HBr] increases). Also, explain how one can write ka, k2r and kar only in terms of Bodenstein's measured experimental values for A1exp and A2exp and concentration based equilibrium constants for reactions 1 and 2. (5 marks)

Answer 1

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