Here's why:
* Breaking bonds requires energy: When ammonium chloride dissolves, the ionic bonds holding the ammonium (NH₄⁺) and chloride (Cl⁻) ions together in the solid need to be broken. This requires energy input.
* Formation of new bonds releases energy: The ions then interact with water molecules, forming new bonds (hydration). However, the energy released in forming these new bonds is less than the energy required to break the original bonds in the solid.
* Net energy change: Since more energy is required to break the original bonds than is released in forming the new bonds, the overall process absorbs energy from the surroundings, leading to a decrease in temperature.
In summary: Dissolving ammonium chloride is an endothermic process, meaning it absorbs heat from the surroundings, causing the temperature of the solution to decrease.
