Question

If the change in entropy $\Delta S$ is positive for an endothermic reaction and the enthalpy change $\Delta H$ occurs at the same temperature $T$, then the reaction is feasible________

• A. at all temperatures
• B. when $\Delta H>T\Delta S$
• C. when $\Delta H<T\Delta S$
• D. not feasible at all

Answer 1

Answer: (C)

when $\Delta H<T\Delta S$

We know the relation, $\Delta G=\Delta H-T\Delta S$, where $\Delta G$ is the change in Gibb's free energy, $\Delta H$ is the change in enthalpy and $\Delta S$ is the change in entropy.

For a feasible reaction, we must have $\Delta G<0$.
$\therefore \Delta H-T\Delta S<0$

$\therefore \Delta H<T\Delta S$, if $\Delta S$ and $\Delta H$ is positive for the reaction.

Hence, the reaction is feasible when $\Delta H<T\Delta S$.

Option C is correct.