Question

Predict the nature of following changes whether exothermic or endothermic?

Dissolution of ammonium chloride in water.

Answer 1

Dissolution of ammonium chloride in water

1. The ammonium chloride$\left({\mathrm{NH}}_4\mathrm{Cl}\right)$ is soluble in water$\left({\mathrm{H}}_2\mathrm{O}\right)$.
2. It dissociates to form the ammonium$\left({\mathrm{NH}}_4^{+}\right)$ and chloride$\left({\mathrm{Cl}}^{-}\right)$ ions.
3. The solution absorbs heat from the surrounding which means the temperature of the solution decreases.

${\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{s}\right)\stackrel{}{\to }{{\mathrm{NH}}_4}^{+}\left(\mathrm{aq}\right)+{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)$

As the compound exists in crystalline form but after dissociation ions move in a random direction which means the entropy increases i.e. positive $∆\mathrm{S}>0$ and the Gibbs energy is negative $∆\mathrm{G}<0$. Hence, the process is spontaneous.

Therefore, the dissolution of ammonium chloride in water is an endothermic change.