jgourlay
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'splain something to me please about water freezing
Gents, here in the office we have a little college refrigerator containing a tiny freezer compartment. For weeks now I've entertained my coworkers
with a never-gets-old stunt.
1. put a bottle of water in the freezer
2. Let it sit long enough to suck out all the latent energy
3. CAREFULLY remove it.
4. Give it a good thump on the side.
5. Watch it instantly crystallize ala the more conventional sodium acetate demonstration.
I understand why this works. What I don't understand is why it doesn't freeze ALL the water. Is the freezing of water slightly exothermic?
Something else?
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kclo4
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Yep freezing water is exothermic since it has to loose all that energy to go from a liquid to a solid. Just like the sodium acetate demonstration is
exothermic, but I think the of hydration also plays a roll, though I am not totally sure, or even sure if that is technically different...
If you can get it colder, while still a liquid it is possible all of it will freeze.. I believe. How much of the water is left afterwords?
Youtube videos of this exist with beer, and a few other things.. might be interested in them. I'd like to get it so it freezes when you open the lid.
That'd be a great trick to play on someone. Watch it freeze right in there hands.. they'd have no idea what was going on 
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JohnWW
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That phenomenon is called supercooling. It happens when a pure and dust-free liquid is cooled to below its normal melting point; despite the lowered
thermal vibrations of the molecules, the amorphous intermolecular structure of the liquid is able to persist in the absence of nuclei, such as dust
particles, on which crystallization can commence. In the case of water, which unusually expands on freezing, supercooling below the normal freezing
point can also be induced by the application of sufficient pressure to prevent it from expanding. It is quite distinct from depression of freezing
points of solvents due to the presence of a solute, which, being proportional to the molar concentration of a solute, can be used as a method for
determining molecular weights.
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Everado E. Dinavo
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That's strange, every bottle of water I've put in the freezer gradually solidifies over time...How much shock does it take to make it crystallize?
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MagicJigPipe
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I'm certain it must be at a certain temperature. There is something called a homogeneous nucleation temperature, at or below which even a pure
substance will crystallize, or freeze.
Basically, there is a "Goldilocks Zone" for this to happen (temperature and pressure) as I understand it.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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ammonium isocyanate
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The true homogeneous nucleation temperature of water is -40*C, so it isn't going to be reached in a regular freezer. However, tap water will freeze
in the absence of external nucleation sources at a much higher temperature due to the solutes dissolved in it. Other factors also influence
nucleation temperature. A smooth bottle will not induce nucleation as easily as a scratched one. Air can also induce nucleation, especially if
pressure is applied to break up a stream of water, as we do in snowmaking (I say we because snowmaking is my other esoteric hobby  ). Certain chemicals (namely proteins) will rapidly induce nucleation even at low
concentration and highish temperatures (currently up to ~-6*C in the snowmaking biz). Using smooth brass for the container I've chilled water to
-10*C without freezing.
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jgourlay
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Everado: sometimes you gotta thump it hard. Open the lid, however, and it goes right off every time.
Thanks gents!
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IrC
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"Basically, there is a "Goldilocks Zone" for this to happen (temperature and pressure)"
Back in the day pepsi was in deposit bottles with crimped on lids this was my favorite summer drink. Put a bottle in the freezer for just the right
time. You could take it out still looking like a clear dark liquid, pop cap off, and it would turn into pepsi freeze just like the stuff in a 7-11
from the machine. You had to drink it fast at first as it was nonstop oozing freeze (freezie? how the hell do you spell that?) which would be painful
going down if you drank it too fast. Best tasting pepsi on earth. Come to think of it pepst has tasted like crap for the last 20 or so years, since I
can no longer find it in deposit bottles. Both the freeze thing and the much better taste I have always thought was due to the greater ability to keep
the carbonation under a higher pressure (without loss) than any modern method the drink is contained today.
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