Steady-state Approximation and Rate-determining Step: ConcepTest and Example Problem

Try to answer this ConcepTest and solve the example problem before using this module. Studies show that trying to answer the questions before studying material improves learning and retention. We suggest that you write down the reasons for your answers. By the end of this module, you should be able to answer these on your own. Answers will be given at the end of this module.

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Example Problem 1

Compare the rate expression obtained by applying the steady-state approximation to a sequence of elementary steps to the measured rate expression.

Overall reaction: \(2A \,+\, B \,\rightleftarrows \,A_2 B\)

Experimental rate expression: \(r_{_{A_2B}} = [0.72(A)^2(B)]/[1 + 2(A)]\)

Elementary steps:

\(A \,+\, B \, \overset{k_1}{\underset{k_{-1}}\rightleftarrows} AB^*\)

\(AB^* \,+\, A \, \overset{k_2}{\underset{k_{-2}}\rightleftarrows} \, A_2B\)