Fagyáspontsüllyedés

Fagyáspontsüllyedés, also known as freezing-point depression, is a colligative property of solutions. This means that the extent to which the freezing point of a solvent is lowered depends on the concentration of solute particles dissolved in it, rather than on the identity of the solute itself.

When a solute is added to a solvent, the solute particles disrupt the ability of solvent molecules to arrange themselves into an ordered crystalline structure that is characteristic of a solid. As a result, a lower temperature is required to freeze the solution compared to the pure solvent. The change in freezing point, ΔTf, is directly proportional to the molality (m) of the solute and a constant known as the cryoscopic constant (Kf) of the solvent. The formula is ΔTf = i * Kf * m, where 'i' is the van't Hoff factor, which accounts for the number of particles a solute dissociates into in solution. For non-electrolytes, i=1.

A common practical application of freezing-point depression is the use of antifreeze in car radiators. Ethylene glycol, a solute, is added to water, the solvent, to lower its freezing point, preventing the water from freezing and damaging the engine in cold weather. Similarly, salt is spread on roads in winter to melt ice, as the dissolved salt lowers the freezing point of water.