Question

Write the overall order of a reaction if A is present in large excess.

Hint:

If one reactant is in excess → pseudo-order reaction. Rate depends only on the limiting reactant.

Answer 1

Concept: If one reactant is present in large excess, its concentration remains nearly constant during the reaction. The reaction then behaves as a
pseudo-order reaction. Given rate law: \[ \text{Rate} = k[A][B]^2 \] If \( A \) is in large excess: \[ [A] = \text{constant} \] Let: \[ k' = k[A] \] Then rate becomes: \[ \text{Rate} = k'[B]^2 \]
Effective order: Now rate depends only on \( [B]^2 \). \[ \therefore \text{Overall order = 2 (pseudo second order)} \]