Here's why:

* Disruption of solvent structure: When a solute dissolves in a solvent, it disrupts the regular arrangement of solvent molecules. This makes it harder for the solvent molecules to form a solid (frozen) structure.

* Solute-solvent interactions: The solute and solvent molecules interact with each other, weakening the attractive forces between solvent molecules and making it less likely for the solvent to freeze.

* Colligative property: Freezing point depression is a colligative property, meaning it depends only on the concentration of solute particles, not their specific identity. The more solute particles there are, the greater the depression in freezing point.

Example:

Adding salt to water lowers the freezing point of the water. This is why salt is used to melt ice on roads in winter. The salt dissolves in the water, lowering the freezing point and preventing the ice from forming.

Formula:

The freezing point depression (ΔTf) can be calculated using the following formula:

ΔTf = Kf * m

where:

* ΔTf is the freezing point depression

* Kf is the freezing point depression constant (a property of the solvent)

* m is the molality of the solution (moles of solute per kilogram of solvent)