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A + B F + G which is catalyzed by reagent C. The rate of this reaction was monit

ID: 922111 • Letter: A

Question

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.

0.000119

0.000316

7.90e-05

5.92e-05

5.92e-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?  


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

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

0.000119

2 0.400 0.0500 0.200

0.000316

3 0.400 0.0500 0.0500

7.90e-05

4 0.300 0.0500 0.0500

5.92e-05

5 0.300 0.100 0.0500

5.92e-05

Explanation / Answer

The most important points from the kinetics

1) Concentration of B has no role in the totoal kinetics compare expeiments 4 and 5 so step 3 cannot be rate limiting.

2) Concentration of both A and C are important as changing these two changes the rate of the reaction.

The rate of the B falling is directly related to the chnages made to either A or C so the step 1 cannot be in equilibrium even if it is fast.

SO the correct answer should be

Step 2 as the rate determining step. All other steps fast steps.