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Freezing Point Depression

What Freezing Point Depression Is and How It Works

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You can lower the freezing point of water into ice using freezing point depression,

You can lower the freezing point of water into ice using freezing point depression,

Thomas Northcut, Getty Images

Freezing point depression occurs when the freezing point of a liquid is lowered by adding another compound to it. The solution has a lower freezing point than that of the pure solvent.

For example, the freezing point of seawater is lower than that of pure water. The freezing point of water to which antifreeze has been added is lower than that of pure water.

Freezing point depression is a colligative property of matter. Colligative properties depend on the number of particles present, not on the type of particles or their mass.

Freezing point depression can be calculated using the Clausius-Clapeyron equation and Raoult's law. In a dilute ideal solution the freezing point is:

Freezing Pointtotal = Freezing Pointsolvent - ΔTf

where ΔTf = molality * Kf * i

Kf = cryoscopic constant (1.86°C kg/mol for the freezing point of water)

i = Van't Hoff factor

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