Question

State a condition under which a bimolecular reaction is kinetically a first-order reaction and give an example.

Hint:

For determining reaction order, observe how the rate changes with concentration. If a bimolecular reaction has an excess reactant, it behaves like a first-order reaction.

Answer 1

Condition for Bimolecular Reaction to Follow First-Order Kinetics A bimolecular reaction follows first-order kinetics when one of the reactants is in excess. In such cases, the reaction appears to be first-order because the concentration of the excess reactant remains nearly constant. Example: Hydrolysis of ester: \[ \text{CH}_3\text{COOCH}_3 + \text{H}_2\text{O} \rightarrow \text{CH}_3\text{COOH} + \text{CH}_3\text{OH} \] Here, water is in large excess, making the reaction effectively first-order.