A condition under which the order of a chemical reaction can be altered is by taking the solvent or the reactant in the excess amount due to which its concentration does not change much.

For example,

CH₃COOCH₃ + H₂0 ⇌ CH₃COOH + CH₃OH

Initially, rate is given by,

Rate= k’ [CH₃COOH] [H₂O]

When we add an excess of solvent then,

Rate= k[CH₃COOCH₃]

Here k= k’[H₂O]

This is also known as pseudo first-order reaction.