Sponaneity and ΔH or ΔS

From $\Delta G = \Delta H - T\,\Delta S$ (at constant $T$ and $P$), the temperature term determines the relative contributions of $\Delta H$ and $\Delta S$ to $\Delta G$:

1. If $\Delta H$ and $\Delta S$ are both negative, then $\Delta G$ will be negative only when $\Delta H$ is more negative than $T\Delta S$. This is possible at low temperatures only.

2. If $\Delta H$ and $\Delta S$ are both positive, $\Delta G$ will be negative only if $T\Delta S > \Delta H$. This is possible only at high temperatures.

3. For $\Delta H$ negative and $\Delta S$ positive, it follows that $\Delta G$ is negative regardless of temperature.

4. For $\Delta H$ positive and $\Delta S$ negative, $\Delta G$ is positive regardless of temperature. Such reactions are nonspontaneous at all temperatures. …