When ammonium chloride dissolves in water, the solution becomes colder. (a) Is the solution process exothermic or endothermic? (b) Why does the solution form?

When ammonium chloride dissolves in water, the solution becomes colder. This indicates that heat is being absorbed from the surroundings, which means the process is endothermic. An endothermic process is one where energy (in the form of heat) is absorbed by the system from its surroundings.

The solution process of ammonium chloride in water is endothermic.

The solution forms as a result of interactions between solute particles (ammonium chloride) and solvent particles (water). Since it is an endothermic process, it suggests that the energy required to break the solute-solute and solvent-solvent interactions is less than the energy released by forming solute-solvent interactions. As water has a high polarity, it can effectively solvate and stabilize the positive ammonium ions (NH4+) and negative chloride ions (Cl-) produced by the dissociation of ammonium chloride. Another important factor is entropy. The natural tendency of a system is to move towards a higher entropy state which means a state with higher randomness or disorder. The dissolution process increases the entropy of the system, as the ions (or molecules) become more dispersed in solution.

The solution forms because the overall energy change and the increase in entropy of the system favor the formation of solute-solvent interactions, leading to the dissolution process.