Question

Although the dissolution of ammonium chloride in water is an endothermic reaction, even then it is spontaneous because:

• A. $\Delta H$ is positive, $\Delta S$ is -ve
• B. $\Delta H$ is +ve, $\Delta S$ is zero
• C. $\Delta H$ is positive, $T\Delta S<\Delta H$
• D. $\Delta H$ is +ve, $\Delta S$ is positive and $\Delta H<T\Delta S$

Answer 1

The correct option is D $\Delta H$ is +ve, $\Delta S$ is positive and $\Delta H<T\Delta S$

Gibb's free energy equation: $\Delta G=\Delta H-T\Delta S$

For a spontaneous reaction, $\Delta G<0$

For endothermic reaction, $\Delta H<0$

For dissolution of ammonium chloride in water, $\Delta S>0$. The magnitude of $T\Delta S$ should be greater than that of $\Delta H$ so that $\Delta G<0$.

Therefore, the dissociation of ammonium chloride in water is an endothermic reaction but is still spontaneous because $\Delta H$ is $+ve$, $\Delta S$ is $+ve$ and $\Delta H<T\Delta S$.