Chemistry - Chemical Kinetics Question with Solution | TestHub

A pseudo-first order reaction is a bimolecular reaction that appears to follow first-order kinetics because one of the reactants is present in large excess, making its concentration essentially constant throughout the reaction.

The acid-catalyzed hydrolysis of methyl acetate is given by the equation:
${\text{CH}}_3{\text{COOCH}}_3+{\text{H}}_2\text{O}\stackrel{{\text{H}}^{+}}{\to }{\text{CH}}_3\text{COOH}+{\text{CH}}_3\text{OH}$

The rate law is expected to be:
$\text{Rate}=k[{\text{CH}}_3{\text{COOCH}}_3][{\text{H}}_2\text{O}]$

Since water is present in large excess, its concentration remains practically constant. The rate law becomes:
$\text{Rate}=k^{\prime }[{\text{CH}}_3{\text{COOCH}}_3]$ where $k^{\prime }=k[{\text{H}}_2\text{O}]$

Thus, it behaves as a first-order reaction and is called a pseudo-first order reaction.

Decomposition of ammonia on platinum metal is a zero-order reaction at high pressure.
Decomposition of ${\text{H}}_2{\text{O}}_2(l)$ and ${\text{N}}_2{\text{O}}_5(g)$ are true first-order reactions.

Answer: Hydrolysis of methyl acetate