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 temperature hence reaction is spontaneous at low temperature.
• D. $\Delta G$ is negative at all temperatures hence reaction is spontaneous at all temperatures.

Answer 1

Answer: (B)

$\Delta G$ is negative at high temperature hence reaction is spontaneous at high temperature.

Answer 2

: $\Delta G = \Delta H - T\Delta S$

For a spontaneous reaction if $\Delta H$is + ve and $\Delta S$ = + ve, $\Delta G$ will be negative when $T\Delta S > \Delta H.$