The rates of many reactions approximately double for each $10^{\circ} \mathrm{C}$ rise in temperature. Assuming a starting temperature of $25^{\circ} \mathrm{C}$, what would the activation energy be, in $\mathrm{kJ} \mathrm{mol}^{-1}$, if the rate of a reaction were to be twice as large at $35^{\circ} \mathrm{C} ?$