Question

Which among the following changes are endothermic or exothermic in nature?

Dissolution of sodium hydroxide in water.

Answer 1

• Endothermic reactions are reactions where energy is absorbed in the form of heat. For example, the melting of ice cubes.
• Exothermic reactions are reactions in which energy is released in the form of heat. For example, Rusting of iron.

Dissolution of sodium hydroxide in water.

When sodium hydroxide is dissolved in water then it breaks down into its corresponding ions i.e. ${\mathrm{Na}}^{+}$and ${\mathrm{OH}}^{-}$with the release of energy in the form of heat.

$\underset{\mathrm{hydroxide}}{\underset{\mathrm{sodium}}{\mathrm{NaOH}\left(\mathrm{aq}\right)}}\to \underset{\mathrm{ion}}{\underset{\mathrm{sodium}}{{\mathrm{Na}}^{+}\left(\mathrm{aq}\right)}}+\underset{\mathrm{ion}}{\underset{\mathrm{hydroxide}}{{\mathrm{OH}}^{-}}}+\mathrm{Heat}$

Since there is the release of heat in this reaction it is an exothermic reaction.