What are pseudo first order reactions ? Give one example.

The reaction whose order is one but molecularity is two is called a pseudo first order reaction.
Eg : (i) Hydrolysis of ethyl acetate :
${\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5+{\mathrm{H}}_2\mathrm{O}\stackrel{{\mathrm{H}}^{+}}{\to } {\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$
Rate of reaction = $\mathrm{k}\left[{\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5\right]$
Here the H₂O is taken in excess. Therefore the rate doesn’t depend on [H₂O]
Order of this reaction is one but molecularity is two.