Question

A2. Chemical Kinetics (20 marks) MBr2 Br Br M k1 |(1) k2. Br H2 HBr H k2,r (2) k3,f HBr2 HBr Br (3) + Experimentally measured rate expression for [HBr] given as below: d [HBr] A1exp[H2] [Br2]1/2 HBr 1+ A2exp TBr2 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 A1,exp 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 Br) 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 Aoxp and A2exp to the rate constants from the elementary reactions above (that is, kf, ki, 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 k2t, k2r and k only in terms of Bodenstein's measured experimental values for A1,0xp and A2exp and concentration based equilibrium constants for reactions 1 and 2. (5 marks)

Answer 1

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