Question

Define Pseudo first order reaction with an example.

Hint:

Pseudo-first-order reactions simplify rate law analysis by holding one reactant constant.

Answer 1

Step 1: In pseudo first order reactions, one reactant is present in large excess so its concentration remains nearly constant during the reaction.
Step 2: As a result, the rate depends effectively only on one reactant, giving an apparent first-order rate law.
Example: \[ \text{Hydrolysis of ester: } CH_3COOC_2H_5 + H_2O \longrightarrow CH_3COOH + C_2H_5OH \] Water is in excess, so the reaction appears to be first-order with respect to ester.