Chemical Kinetics

For the reaction

\(\mathrm{N}_{2(\mathrm{~g})}+3 \mathrm{H}_{2(\mathrm{~g})} \longrightarrow 2 \mathrm{NH}_{3(\mathrm{~g})}\)

$\mathrm{N}_{2(\mathrm{~g})}$ disappears at the rate of $2 \times 10^{-4} \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{~s}^{-1}$. Find the rate of $\mathrm{NH}_3$ formation.