Freezing point depression

[yjj8817]

So I'm reading about this in tbr and it says that when you put salt on ice cube, the water molecules from the ice are attracted to it and are removed from the ice. It says that this process is exothermic, and this releases more energy to melt the ice further. Why is it exothermic? I thought melting was endothermic? Thanks!

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[Cawolf]

The formation of bonds is an exothermic process.

They are likely referring to the salt ions forming hydrogen bonds with water - which would release energy.

 

[Eaglefan]

Freezing point is a colligative property-- more molecules (via adding) salt will depress the freezing point. so now the ice is above its freezing point and will melt. The dissolution of salt is exothermic, but the melting is still endothermic, I think? This is an interesting question

 

[yjj8817]

The formation of bonds is an exothermic process.

They are likely referring to the salt ions forming hydrogen bonds with water - which would release energy.

If this is the case, why doesn't that help with boiling process? Shouldn't the released energy make the process easier since there would be more energy?

 

[Cawolf]

If the water is near it's boiling point, it now has to break those bonds formed during solvation. You have water molecules weakly bonded to ions in the solution.

So it requires more energy to break free from the liquid - raising the boiling point.

In general adding a solute to a pure liquid will make the liquid "want" to stay a liquid by lowering the freezing point and raising the boiling point.