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.
For the spontaneity of a reaction, which statement is true?

Options

A. `Delta G =" + ve, "Delta H = +ve`
B. `Delta H =+ ve, Delta S= -ve`
C. `Delta G =-ve, Delta S =-ve`
D. `Delta H =-ve, Delta S = +ve`

Answer

D

Explanation

For spontaneous process `Delta S_("total")` is positive.