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 :
$$\Delta G$$ is negative at high temperature hence reaction is spontaneous at high temperature.
Solution :
$$\Delta G = \Delta H - T\Delta S$$
For a spontaneous reaction if $$\Delta H$$ is $$ + ve$$ and $$\Delta S = + ve,\Delta G$$ will be negative when $$T\Delta S > \Delta H.$$