Chemistry - Thermodynamics - II Question with Solution | TestHub

Explain Question:

To determine which condition is not favorable for the feasibility (spontaneity) of a process.

Concept:

Spontaneity and feasibility are determined by the Gibbs free energy change, $\Delta G$.

The relationship is given by the equation:

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

A process is spontaneous if $\Delta G<0$.

Solution:

Analyzing the given options:

1. $\Delta H=–ve$, $T\Delta S=–ve$, and $|T\Delta S|<|\Delta H|$

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

* Since $\Delta H$ is negative (exothermic) and $T\Delta S$ is also negative, the reaction will be spontaneous if $|\Delta H|>|T\Delta S|$.

* Favorable (Spontaneous).

2. $\Delta H=+ve$, $T\Delta S=+ve$, and $T\Delta S>\Delta H$

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

* Since $T\Delta S$ is larger than $\Delta H$, $\Delta G$ becomes negative, making the process spontaneous.

* Favorable (Spontaneous).

3. $\Delta H=–ve$, $T\Delta S=+ve$, and $|\Delta H|>|T\Delta S|$

* $\Delta G=\Delta H-T\Delta S=–ve$ (always)

* Hence, the process is spontaneous.

4. $\Delta H=+ve$, $T\Delta S=+ve$, and $\Delta H<T\Delta S$

* $\Delta G=\Delta H-T\Delta S=+ve$ (Non-spontaneous)

* Hence, this condition is not favorable for feasibility.

Final Answer: Option (D)