For a reaction to be spontaneous, the change in Gibbs free energy ($\Delta G$) must be negative ($\Delta G < 0$). We know that, $\Delta G = \Delta H - T\Delta S$ For $\Delta G < 0$, $\Delta H - T\Delta S < 0 \implies T > \frac{\Delta H}{\Delta S}$ Given: $\Delta H = 35.5 \text{ kJ/mol} = 35500 \text{ J/mol}$ $\Delta S = 83.6 \text{ J/K}\cdot\text{mol}$ Substituting the values: $T > \frac{35500}{83.6} \text{ K}$ $T > 424.64 \text{ K}$ Thus, the reaction is spontaneous at temperatures greater than $425 \text{ K}$ (i.e., $T > 425 \text{ K}$) .