Question

Free energy, $G=H-TS$, is a state function that indicates whether a reaction is spontaneous or nonspontaneous. If you think of $TS$ as the part of the system's energy 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, $\Delta G=\Delta H-T\Delta S$
From the second law of thermodynamics, a reaction is spontaneous if ${\Delta }_{\text{total }}S$ is positive, non-spontaneous if ${\Delta }_{\text{total }}S$ is negative, and at equilibrium if ${\Delta }_{\text{total }}S$ is zero.
Since, $-T\Delta S=\Delta G$ and since $\Delta G$ and $\Delta S$ have opposite signs, we can restate the thermodynamic criterion for the spontaneity of a reaction carried out a constant temperature and pressure
If $\Delta G<0$, the reaction is spontaneous
If $\Delta G>0$, the reaction is non-spontaneous
If $\Delta G=0$, 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?

• 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 1

Answer: (D)

$\Delta H=-$ ve and $\Delta S=+$ ve, both favour the process