# Thread: Where does freezing water get its kinetic energy from?

1. We all know water expands as it turns to ice. This expansion can be enough to break water storage vessels, like water bottles. If the energy is being taken away to freeze the water, where does the energy come from to break a bottle?

2.

3. Originally Posted by Gen1GT
We all know water expands as it turns to ice. This expansion can be enough to break water storage vessels, like water bottles. If the energy is being taken away to freeze the water, where does the energy come from to break a bottle?
The energy isn't being "taken away", it is "given up". That energy has to go somewhere, and that is the energy that breaks the vessel. This Energy is the Latent heat, and is 334,000 J/kg for water.

This latent heat used to be used by farmers back when they stored vegetables in root cellars. They would place large barrels of water in the cellars with the vegetables. This way, the latent heat given up by the water as it froze protected the vegetables.

4. I don't want to complain, but isn't this a somewhat peculiar way to look at it?
I would say that the water freezes when it has been in thermal contact with some body of a temperature below zero long enough to give off its latent heat - not in the reversed order.
I also thought that the farmers placing barrels of water in their cellars, was because the large specific heat capacity of water would prevent great drops in temperature.

5. there is no "kinetic" energy that's 1/2MV^2.
expansion of ice is due to the heagonal lattice structure occupying more volume than the liquid.

6. Originally Posted by thyristor
I don't want to complain, but isn't this a somewhat peculiar way to look at it?
I would say that the water freezes when it has been in thermal contact with some body of a temperature below zero long enough to give off its latent heat - not in the reversed order.
I also thought that the farmers placing barrels of water in their cellars, was because the large specific heat capacity of water would prevent great drops in temperature.
I believe Janus is correct. The latent heat is released as the water freezes and this would help maintain a constant air temperature at 0degC until all the water is frozen. After that the heat capacity of the solid ice would probably help to slow the temperature drop.

The corresponding reverse effect that's more intuitive would be evaporation of sweat from the skin. The latent heat of vaporization cools the skin.

7. Originally Posted by Gen1GT
We all know water expands as it turns to ice. This expansion can be enough to break water storage vessels, like water bottles. If the energy is being taken away to freeze the water, where does the energy come from to break a bottle?
When water freezes it's temperature remains constant. Because the temperature is not changing- this energy goes into forming hydrogen bonds which are intermolecular bonds. Bond forming releases heat.

Because the temperature is constant - energy is going into forming bonds which cause the expansion.

9. Originally Posted by Bunbury
Originally Posted by thyristor
I don't want to complain, but isn't this a somewhat peculiar way to look at it?
I would say that the water freezes when it has been in thermal contact with some body of a temperature below zero long enough to give off its latent heat - not in the reversed order.
I also thought that the farmers placing barrels of water in their cellars, was because the large specific heat capacity of water would prevent great drops in temperature.
I believe Janus is correct. The latent heat is released as the water freezes and this would help maintain a constant air temperature at 0degC until all the water is frozen. After that the heat capacity of the solid ice would probably help to slow the temperature drop.

The corresponding reverse effect that's more intuitive would be evaporation of sweat from the skin. The latent heat of vaporization cools the skin.
What I mean is that the latent heat isn't released as the water freezes, the water freezes as the latent heat is released. The freezing of water does, as far as I know but I may very well be wrong, not work in the same way as the solidification of the compounds in heat bags. There, the solidification is initiated by adding the initiation energy to it, and here you could really say that it gives off its latent heat as it freezes.

10. Originally Posted by Gen1GT
We all know water expands as it turns to ice. This expansion can be enough to break water storage vessels, like water bottles. If the energy is being taken away to freeze the water, where does the energy come from to break a bottle?
The water contains more energy than the ice in one kilogram. When water freezes, it releases its energy, one kind of which is to work to the environment. The mechenism that rules the solification is not to make sure the energy minimizes but the chemical potential minumizes, for the pressure remains. And this mechanism forces the phase transition occure.

11. Ice (solid H2O) is less dense than water (which is why ice floats). The reason for this has to do with the molecular structure of water. Ice is what is called a "true solid"; meaning it has a crystal lattice structure. Obviously, when water is in its liquid form, there is no crystal lattice/structure.

When water begins to freeze, the molecules space apart just enough to create a hydrogen-bond attraction - between hydrogen atoms of one molecule to oxygen atoms on the other molecule - and create a crystal lattice. This is why water expands and this is the cause of the container breakage....from water forming a lattice structure.

Where does the energy come from?
The answer is attractive forces (magnetic) between the molecules themselves. Water molecules are polar; meaning they have a positive side and a negative side. When the crystal lattice arranges itself during freezing, it is easier for the molecules to settle and form a lattice structure.

Although the release of energy has SOMETHING to do with it, it doesn't affect the container to the point of breakage....in my opinion.

12. Originally Posted by shckm2686
The water contains more energy than the ice in one kilogram.
Just one little nit-pick, but one kilogram exactly of any substance has exactly the same amount of energy (e=mc^2). It is more correct to say that one mole of water has more energy than one mole of ice.

13. Originally Posted by Reaper
The answer is attractive forces (magnetic) between the molecules themselves
Electric, actually, rather than magnetic, but otherwise

Originally Posted by Reaper
Although the release of energy has SOMETHING to do with it, it doesn't affect the container to the point of breakage....in my opinion.
As the water crystallises, the polar regions allign themselves into such a pattern as to hold the minimum potential energy in the molecules. Decreasing the potential energy means work is done by the water; giving the water kinetic energy which, in an unconfining vessel, would be lost mostly as heat. In an enclosed space, on the other hand, the kinetic energy goes into breaking the container, or if the container is too strong, then the molecules cannot allign to start with, so this latent heat cannot be released. Therefore, the water will not freeze under pressure, although it will become very viscous.

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