For a given reaction $2\mathrm{N}\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\rightleftharpoons 2{\mathrm{N}\mathrm{O}}_2\left(\mathrm{g}\right)$
Rate of reaction $=\mathrm{k}\left[\mathrm{N}\mathrm{O}{]}^2\right[{\mathrm{O}}_2]$
Rate of reaction is directly proportional to concentration of the compound or inversely proportional to the volume of the vessel.
i.e.,
$\mathrm{C}\propto \frac{\mathrm{n}}{\mathrm{V}}$
If volume of vessel is reduced by $1/3$ rd of its initial value, then concentration of compound is increased by 3 times and consequently the rate of reaction increases by 27 times.