Free enegry , `G = H - TS`, is state function that indicates whther a reaction is spontaneous or non-spontaneous. If you think of `TS` as the part of the system's enegry that is disordered already, then `(H -TS)` is the part of the system's energy that is still ordered and therefore free to cause spontaneous change by becoming disordered.
Also, `DeltaG = DeltaH - T DeltaS` From the second law of thermodynamics, a reaction is spontaneous if `Delta_("total")S` is positive, non-spontaneous if `Delta_("total")S` is negative, and at equilibrium if `Delta_('total")S` is zero.
Since, `-T DeltaS = DeltaG` and since `DeltaG` and `DeltaS` have opposite sings, we can restate the thermodynamic criterion for the spontaneity of a reaction carried out a constant temperature and pressure.
IF `DeltaG lt 0`, the reaction is spontaneous.
If `DeltaG gt 0`, the reaction is non-spontaneous.
If `DeltaG = 0`, the reaction is at equilibrium.
Read the above paragraph carefully and answer the following questions based on the above comprehension.
If an endothermic reaction is non-spontaneous at freezing point of water and becomes feasible at its boiling point, then

Options

A. `Delta H" is -ve "Delta S` is +ve`
B. `Delta H and Delta S` both are +ve
C. `Delta H and Delta S` both are -ve
D. `Delta H" is +ve " and Delta S` is -ve

Answer

B

Explanation

For endothermic reaction, `Delta H` is + ve as `Delta G= Delta H-T Delta S, Delta G` is + ve at low temperature, if `Delta S` is + ve but `T Delta S lt Delta H.` At high temperature `T Delta S gt Delta H and Delta G` becomes - ve.