Question

Part G What is the rate law predicted by this mechanism? Use a for [(CH3)3AuPH3], b for [(CH3)3Au], c for [PH3], d for [C2H6], e for [(CH3)Au] and k for the rate constant.

In a hydrocarbon solution, the gold compound (CH3)3AuPH3(CH3)3AuPH3 decomposes into ethane (C2H6C2H6) and a different gold compound, (CH3)AuPH3(CH3)AuPH3. The following mechanism has been proposed for the decomposition of (CH3)3AuPH3(CH3)3AuPH3:
Step 1: (CH3)3AuPH3⇌(CH3)3Au+PH3(fast)(CH3)3AuPH3⇌(CH3)3Au+PH3(fast)
Step 2: (CH3)3Au→C2H6+(CH3)Au(slow)(CH3)3Au→C2H6+(CH3)Au(slow)
Step 3: (CH3)Au+PH3→(CH3)AuPH3(fast)

Answer 1

The overall reaction in this case will be

The rate determining step will be governed by the slowest step in the reaction

(The slow one in this case will be second step)

Rate of forward reaction = Rate of backward reaction

Hence the predicted rate law mechanism will be

Hence the correct answer will be Option b