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For a given reaction, $\Delta H$ = 35.5 kJ $mol^{-1}$ and $\Delta S$ = 83.6 $JK^{-1} mol^{-1}$. The reaction is spontaneous at: (Assume that $\Delta H$ and $\Delta S$ do not vary with temperature)
Explanation
Endothermic with positive $\Delta S$: spontaneous above $\Delta H/\Delta S$.
Detailed Solution
$\because \Delta G = \Delta H - T\Delta S$
For a reaction to be spontaneous, $\Delta G$ = –ve, i.e. $\Delta H \frac{\Delta H}{\Delta S} = \frac{35.5\times10^3\ J}{83.6\ JK^{-1}}$
i.e. T > 425 K