Question

$\Delta G$ is the net energy available to do useful work and is a measure of free energy. If a reaction has positive enthalpy change and positive entropy change, under what conditions will the reaction be spontaneous?

• A. $\Delta G$ will be positive at low temperature hence reaction is spontaneous at low temperature
• B. $\Delta G$ is negative at high temperature hence reaction is spontaneous at high temperature
• C. $\Delta G$ is negative at low temperatue hence reaction is spontaneous at low temperature
• D. $\Delta G$ is negative at all temperatures hence reaction is spontaneous at all temperatures

Answer 1

The correct option is B $\Delta G$ is negative at high temperature hence reaction is spontaneous at high temperature

As We Know,
$\Delta G=\Delta H-T\Delta S$
For a spontaneous reaction if $\Delta H$ is $+ve$ and $\Delta S=+ve$, $\Delta G$ will be negative when $T$ is High so, $T\Delta S>\Delta H$.
Hence, Option (b) is Correct.