When ammonium chloride (NH₄Cl) dissolves in water (H₂O), it undergoes a dissociation reaction producing ammonium ions (NH₄⁺) and chloride ions (Cl⁻).

Here's the chemical equation:

NH₄Cl(s) + H₂O(l) → NH₄⁺(aq) + Cl⁻(aq)

This reaction is endothermic, meaning it absorbs heat from the surroundings. As a result, the solution becomes cooler than the original water.

Explanation:

* Ammonium chloride is a salt formed from the reaction of a weak base (ammonia, NH₃) and a strong acid (hydrochloric acid, HCl).

* In water, ammonium chloride dissociates into its constituent ions, ammonium (NH₄⁺) and chloride (Cl⁻).

* Ammonium ions can further react with water molecules in a reversible equilibrium to produce hydronium ions (H₃O⁺) and ammonia (NH₃). This reaction makes the solution slightly acidic due to the presence of hydronium ions.

Overall, the reaction of ammonium chloride and water results in a slightly acidic solution, a decrease in temperature, and the formation of ammonium ions, chloride ions, and a small amount of hydronium ions.