Question

Why does the temperature of solution change marginally upon addition of sodium chloride to water?

Answer 1

Because the dissolution of sodium chloride is ONLY slightly endothermic.

Explanation:

`NaCl(s) + excess H_2O rarr Na^(+)(aq) + Cl^(-)(aq)`

This reaction is very slightly endothermic. The energy required to breakup the ionic lattice is ALMOST balanced by the formation of ion-dipole bonds between the ion and the solvent water molecules. For other salts, for instance sodium hydroxide, or ammonium chloride, dissolution in water is strongly exothermic (`NaOH`) or strongly endothermic (`NH_4Cl)`.