Question

A reaction A$_2$ + B$_2$ → 2AB occurs by the following mechanism:
A$_2$ → A + A (slow)
A + B$_2$ → AB + B (fast)
A + B → AB (fast)
Its order would be:

• A. 1
• B. 2
• C. Zero
• D. \( \frac{1}{2} \)

Hint:

In multi-step reactions, the slowest step determines the reaction order, as it is the rate-limiting step.

Answer 1

The Correct Option is A

Since the rate-determining step is the first step (A$_2$ → A + A), the rate law depends only on A$_2$. Thus, the reaction follows first-order kinetics with respect to A$_2$, making the overall reaction first order.