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Q & A: Turning water into ice at room temperature

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Most recent answer: 10/22/2007
Q:
How can a normal bottle of mineral water at room temperature turn into ice?
- Mary
robinson
A:
Hi Mary,

Good question! A substance's state can normally be a solid, liquid, or gas, depending on its temperature and pressure. (I'll talk only about pure water for the moment, and your bottle of mineral water may indeed have less dissolved stuff in it than some tap waters.)

The molecules in a gas are loosly arranged and move freely, colliding with each other occasionally. The molecules in a liquid are constantly interacting with their neighbors, but they still have too much energy to settle down. The molecules in a solid are locked in a rigid pattern in space and for most substances are closer together on average in the solid than they are in the liquid. Water is an exception to this -- it expands when it freezes at ordinary pressure, which is why ice floats on the top of a frozen lake. And also why you will break a glass bottle of mineral water if you put it in the freezer.

So for most substances, (except water for now, I'll get back to it!) you can get them to solidify at room temperature if you squeeze on them hard enough, forcing the molecules to get close together and arrange themselves in the rigid solid pattern. Water's the peculiar one and it works backwards -- you can get ice to melt by squeezing on it! See our answer to this question: .

So you might think this one's hopeless. But have no fear, ordinary water has even more surprises locked up inside of it,if you squeeze it *really really really* hard. I'm getting this information from . Room temperature is about 300 K, so squeezing the water to a pressure of one billion Pascals -- about 10,000 atmospheres or the pressure you'd get under 64 miles of water (if there were such a place), then the water at room temperature will turn to ice, and your bottle will be broken. The funny thing is that the ice won't be the usual ice we get in our freezers, but one with a different ordering pattern for the water molecules (the ordinary one takes up too much space).

So, yes, you can do it, but it is really difficult. A more popular demonstration sometimes done is a bit of a cheat on this question but also illustrates some fun physics. If you pump all of the air out of the bottle with a vacuum pump, then the water inside will start to boil. It takes heat energy to release a water molecule from the liquid to the gas, and so the whole thing cools down when this happens. Eventually the remaining water will get cold enough to freeze, which is very entertaining because it is done without the aid of a freezer. It isn't quite the answer to your question, because the water gets very cold in the process, and so this whole thing doesn't happen at room temperature as asked. Also, the time I saw it done was with a small amount of water in a very tiny dish -- it may be hard to get a bottle of mineral water to work because heat may leak in through the sides faster than it can be removed by the boiling.

Tom

(published on 10/22/2007)

Follow-Up #1: freezing via evaporation

Q:
Hello Guys,
I witnessed on TV exactly what you’ve described, freezing water by vacuum boiling. The demonstration was mind boggling and dramatic! It consisted of a large (12" dia.)glass spherical beaker with a long glass stem (3’ by 2") connected to a vacuum pump. The long stem was angled sideways about 30* above horizon; perhaps to allow heavy vapor to escape easier.
The large spherical beaker was 1/2 full of water. After a brief discussion the vacuum pump was turned on. The water froze in 7 seconds!!! Please, please help me find this video for my college students so that I may duplicate it.
- Michael Marsden, Ph.D. (age 40)
S.P.I., Tx. , USA
A:
Hi Mike- I found a video link that shows this process, although it is misleadingly labeled 'freezing at room temperature'



Mike W.

(published on 10/22/2007)

Follow-up on this answer.