Why does salt lower the freezing point of water?

The freezing point depression is explained quite well on the wikipedia page describing the phenomenon (http://en.wikipedia.org/wiki/Fre… ):

The explanation for the freezing point depression is then simply that as solvent molecules leave the liquid and join the solid they leave behind a smaller volume of liquid in which the solute particles can roam. The resulting reduced entropy of the solute particles thus is independent of their properties.
In the extreme situation, completely freezing a mixture of water and salt leaves pure ice and pure salt crystals. The mixture has been unmixed. This unmixing is something compounds do not "like": the universe likes to be uniform (strangely enough, a uniform mixture is maximizing "chaos" in the sense of physics, this is also called "entropy"). Thermodynamics teaches that a loss in entropy can be overcome by a gain in so called "enthalpy". The loss of entropy by freezing the solution can be overcome at temperatures much below 0 degrees Celsius because the gain in enthalpy by freezing water rises when the temperature goes down.

I think this is quite different from the considerations about the boiling point by Judy Levy Pordes.

Answer by Rob Hooft:

The freezing point depression is explained quite well on the wikipedia page describing the phenomenon (http://en.wikipedia.org/wiki/Freezing-point_depression ):

The explanation for the freezing point depression is then simply that as solvent molecules leave the liquid and join the solid they leave behind a smaller volume of liquid in which the solute particles can roam. The resulting reduced entropy of the solute particles thus is independent of their properties.

In the extreme situation, completely freezing a mixture of water and salt leaves pure ice and pure salt crystals. The mixture has been unmixed. This unmixing is something compounds do not "like": the universe likes to be uniform (strangely enough, a uniform mixture is maximizing "chaos" in the sense of physics, this is also called "entropy"). Thermodynamics teaches that a loss in entropy can be overcome by a gain in so called "enthalpy". The loss of entropy by freezing the solution can be overcome at temperatures much below 0 degrees Celsius because the gain in enthalpy by freezing water rises when the temperature goes down.

I think this is quite different from the considerations about the boiling point by Judy Levy Pordes.

Why does salt lower the freezing point of water?

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