Freezing-point depression

Freezing-point depression is the lowering of a solvent’s freezing temperature when a solute dissolves in it. In dilute solutions, the change is proportional to the dissolved particles’ concentration.

Colligative properties: Solution properties determined by the number of dissolved particles rather than their chemical identity. Freezing-point depression is one of the properties governed chiefly by dissolved-particle concentration.
Antifreeze: A substance added to a liquid to lower its freezing point and help prevent freezing. Automotive antifreeze uses dissolved solutes to keep engine coolant liquid below water’s freezing point.
Phase transition: A change between distinct physical states of matter, such as solid, liquid, and gas. Freezing-point depression shifts the temperature of the liquid-to-solid transition.
Boiling-point elevation: The increase in a solvent’s boiling temperature caused by dissolving a nonvolatile solute. It is the paired colligative effect at the liquid–vapor boundary rather than the solid–liquid boundary.
Chemical potential: A thermodynamic quantity measuring how a system’s free energy changes when a component is added. Dissolved solute lowers the solvent’s chemical potential in the liquid, shifting solid–liquid equilibrium.
Road salt: Salt spread on roads to reduce ice formation and help melt existing ice. Dissolved salt lowers water’s freezing temperature, though its effectiveness depends on temperature and concentration.
Freezing: The phase transition in which a liquid becomes a solid. The depressed temperature is the condition at which solvent freezing begins in a solution.
Osmotic pressure: The pressure required to stop solvent flow across a semipermeable membrane. It is another colligative property, arising from the same solvent chemical-potential change.
Freezing-point constant: A solvent-specific constant relating freezing-point change to the molality of a dilute solution. It sets how strongly a given solvent’s freezing temperature responds to dissolved particles.
Cryoscopy: A method for determining a solution’s properties by measuring its freezing-point change. The size of the shift can reveal the concentration or molar mass of a dissolved substance.

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