Question

The reaction \( \text{A}_2 + \text{B}_2 \to 2\text{AB} \) follows the mechanism: \[ \text{A}_2 \xrightarrow{k_1} \text{A} + \text{A} \, (\text{fast}), \quad \text{A} + \text{B}_2 \xrightarrow{k_2} \text{AB} + \text{B} \, (\text{slow}), \quad \text{A} + \text{B} \to \text{AB} \, (\text{fast}). \] The overall order of the reaction is:

• A. 3
• B. 1.5
• C. 2.5
• D. 2

Hint:

The overall order of a reaction is determined by the rate-determining step and the exponents of the reactants in that step.

Answer 1

The Correct Option is B

- The slow step in the mechanism (\( \text{A} + \text{B}_2 \to \text{AB} + \text{B} \)) dictates the overall order of the reaction.
- The order with respect to A is 1, and with respect to B₂ is 0.5 (due to the formation of AB from B₂ in the slow step). 
Thus, the overall order of the reaction is 1.5.