Question

Consider the following reaction mechanism:

Step 1:
(CH3)3AuPH3 (CH3)3Au + PH3 (fast)
Step 2:
(CH3)3Au → C2H6+(CH3)Au (slow)
Step 3:
(CH3)Au + PH3 → (CH3)AUPH3 (fast)

Which step is the
rate-determining step?

a. step 1
b. step 2
c. step 3​

Answer 1

Answer: B

Step-by-step explanation:

In the rate law, the rate- determining step is the slow step.

Answer 2

• Step 2 (the slow step).

Step-by-step explanation:

The rate-determining step is always the slow step of a mechanism.

That is so, because it is the slow step which limits the reaction.

Imaging that for assembling a toy you have process of three steps:

• 1. order ten pieces, which you can do in 1 minute: meaning that you can order order the pieces for 60/1 = 60 toys in 1 hour.

• 2. glue the pieces and hold the toy until the glue hardens, which takes 1 hour: meaning finishingh 1 toy in 1 hour.

• 3. pack the toy, which takes 2 minutes: meaning that you can pack 60/2 = 30 toys in one hour.

The time to glue and hold one toy until the glue hardens determines that you can assemble 1 toy in 1 hour and not 60 toys or 30 toys.

Thus, the step that determines the rate at which the reaction happens is the slowest step: step 2.