When a solute is added to a solution, there will be a boiling point elevation (or increase), a freezing point depression (or lowering), and vapor pressure lowering. These are called colligative properties of a solution because it only depends on the number of solute particles added and not on the nature of the solute.
For boiling point elevation, when a solute is added, more solute-solvent intermolecular forces will exist thus more energy is needed to break these bonds, and in turn increases the boiling point of the solution.
For freezing point depression, more Kinetic energy must be withdrawn from the solution because the solute is surrounded by solvent molecules. They hinder the formation of a solid in the solution.
For Vapor pressure lowering, the presence of more solute particles hinder some solvent molecules to vaporize.
