Final answer:
Dissolving sodium chloride in water is an endothermic and physical process that increases entropy. It is driven by ion-dipole interactions and leads to a colder solution. When saturation is reached, dissolution and recrystallization are balanced in a dynamic equilibrium.
Step-by-step explanation:
The process of sodium chloride (NaCl) dissolving in water and causing the solution to get colder is an endothermic reaction. It is associated with an increase in entropy, and the dissolution is considered a physical change. This reaction is endothermic because the dissolution absorbs heat from the surroundings, which is why the temperature of the solution decreases.
NaCl dissolves into its constituent ions in water due to the polar nature of water molecules. The positive Na+ ions are attracted to the negative poles of the water molecules, and the negative Cl- ions are attracted to the positive poles. This ion-dipole interaction results in the dissociation of the salt into individual ions that become hydrated in the solution.
When NaCl dissolves, it reaches a point of saturation, where no more salt can dissolve and excess remains at the bottom. However, even at saturation, the solution is dynamic: the process of dissolution and recrystallization continues without affecting the observable concentration, meaning that the forward (dissolving) and reverse (recrystallizing) processes are in equilibrium.