Question

Dissolution of ammonium chloride in water is an endothermic reaction, yet it is a spontaneous process. This is due to the fact that :

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

Answer 1

Answer: (C)

$\Delta$H is +ve, $\Delta$S is +ve and $\Delta$H < T$\Delta$S

$\Delta H>0$ (endothermic reaction)

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

For spontaneous process, $\Delta G<0$

Therefore, $\Delta G=\Delta H-T\Delta S<0$

But $\Delta H>0$

Therefore for $\Delta G$ to be negative, $\Delta S>0$ and $\Delta H<T\Delta S$.