MHTCET 23 Apr 2025 Shift 2 Paper

Concept:A reaction is spontaneous when $\Delta G < 0$, where $\Delta G = \Delta H - T\Delta S$.The phrase "spontaneous below equilibrium temperature" means the reaction occurs only at temperatures lower than the equilibrium temperature $T_{eq}$.Explanation:At equilibrium, $\Delta G = 0$.Therefore, $T_{eq} = \frac{\Delta H}{\Delta S}$.For spontaneity only below $T_{eq}$, the reaction must become non-spontaneous at higher temperatures.This condition is satisfied when $\Delta H < 0$ and $\Delta S < 0$.At low $T$, the negative $\Delta H$ term dominates, so $\Delta G < 0$ and the reaction is spontaneous.At high $T$, the positive $-T\Delta S$ term dominates, so $\Delta G > 0$ and the reaction is non-spontaneous.Thus, spontaneity occurs only below the equilibrium temperature.Verify the other options:$\Delta H < 0$, $\Delta S > 0$: spontaneous at all temperatures.$\Delta H > 0$, $\Delta S > 0$: spontaneous only above $T_{eq}$.$\Delta H > 0$, $\Delta S < 0$: non-spontaneous at all temperatures.Answer:Option A: $\Delta H < 0$ and $\Delta S < 0$.