Consider the reaction: Consider the fictional reaction: A + B F + G which is cat

Question

Consider the reaction:

Consider the fictional reaction:

A + B F + G

which is catalyzed by reagent C.

The rate of this reaction was monitored by looking at the disappearance of B under several different experimental setups at 298 K.

0.000107

0.000286

7.14e-05

5.36e-05

5.36e-05

Step 1: A + C D
Step 2: D E + C
Step 3: E + B F + G

Given the previous information, which of the following situations would lead to a plausible reaction mechanism?  


Incorrect Step 2 as the rate determining step. All other steps fast steps.
Incorrect Step 3 as the rate determining step. All other steps fast steps.
Incorrect Step 3 as the rate determining step. Step 2 is a fast equilibrium step while step 1 is a fast step.
Correct: Step 2 as the rate determining step. Step 1 is a fast equilibrium step while step 3 is a fast step.

How is this the answer and how is the fast equilibrium step determined???

Experiment [A]
(M) [B]
(M) [C]
(M) Rate of disappearance of B
(M/s) 1 0.300 0.0500 0.100

0.000107

2 0.400 0.0500 0.200

0.000286

3 0.400 0.0500 0.0500

7.14e-05

4 0.300 0.0500 0.0500

5.36e-05

5 0.300 0.100 0.0500

5.36e-05

Explanation / Answer

From the above data,catalyst influencing rate of disappearance of B effectively and also from reaction mechanism formation of D is fast equilibrium step,due to it is activated complex step(reactant + catalyst =activated complex)which maintains required activation energy and retaining catalyst is slow step (step2)by liberating high energitic E.Then formation of F and G is fast step reaction due to high energy of E reactant.

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