For the reaction
$$\mathrm{N}_{2} \mathrm{O}_{5}(\mathrm{~g}) \longrightarrow 2 \mathrm{NO}_{2}(\mathrm{~g})+\frac{1}{2} \mathrm{O}_{2}(\mathrm{~g})$$
the rate constant $k$ at $25^{\circ} \mathrm{C}$ is $3.46 \times 10^{-5} \mathrm{~s}^{-1}$ and at $55^{\circ} \mathrm{C}$ it is $1.5 \times 10^{-3} \mathrm{~s}^{-1} .$ Calculate the activation energy, $E_{\mathrm{a}}$.