The following concentrations were observed at $500 \mathrm{~K}$ for the formation of $\mathrm{NH}_3$ from $\mathrm{N}_2$ and $\mathrm{H}_2$. At equilibrium ; $\left[\mathrm{N}_2\right]=2 \times 10^{-2} \mathrm{M},\left[\mathrm{H}_2\right]=3 \times 10^{-2} \mathrm{M}$ and $\left[\mathrm{NH}_3\right]=1.5 \times 10^{-2} \mathrm{M}$. Equilibrium constant for the reaction is ________.