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AP Chemistry
5.11 Catalysis
5.10 Multistep Reaction Energy Profile
5.8 Reaction Mechanism and Rate Law
5.7 Introduction to Reaction Mechanisms
5.6 Reaction Energy Profile
AdvancedMCQGraphicalConceptual24.5k
Reaction energy profiles for the original (solid) and modified (dashed) catalyzed pathways.
Reaction energy profiles for the original (solid) and modified (dashed) catalyzed pathways.
An aqueous reaction \(\text{A(aq)} + \text{B(aq)} \rightarrow \text{P(aq)}\) is catalyzed by an enzyme \(\text{E}\) according to the following proposed three-step mechanism:

\[ \text{Step 1: } \text{E(aq)} + \text{A(aq)} \rightleftharpoons \text{I}_1\text{(aq)} \quad \text{(fast)} \]
\[ \text{Step 2: } \text{I}_1\text{(aq)} + \text{B(aq)} \rightarrow \text{I}_2\text{(aq)} \quad \text{(slow, rate-determining)} \]
\[ \text{Step 3: } \text{I}_2\text{(aq)} \rightarrow \text{P(aq)} + \text{E(aq)} \quad \text{(fast)} \]

The reaction energy profile for the original enzyme-catalyzed reaction is shown by the solid curve. A genetically modified variant of the enzyme selectively stabilizes intermediate \(\text{I}_1\), lowering its potential energy as shown by the dashed curve, while the energies of the reactants, products, and all transition states (\(\text{TS}_1\), \(\text{TS}_2\), and \(\text{TS}_3\)) remain unchanged.

Which of the following correctly predicts the effect of this modification on the activation energy of Step 2 (\(E_{a,2}\)) and the overall rate of product formation?

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