Naked Science Forum
General Science => General Science => Topic started by: petrovitch on 15/08/2008 18:57:38
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I freeze bottled water daily; frequently, several bottles remain in a liquid state for several days while adjacent bottles crystalize into ice. When I shake these bottles they snap freeze from top to bottom, layer by layer into a solid bottle of ice.
[???] How can water remain in a liquid state below 32 degrees Fahrenheit?
[???] Is this an example of super cooling?
[:)] It is absolutely amazing to see this happen.
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Yes, it's super cooling. We must remember that most of the laws we know of chemistry, and even of physics, are valid at equilibrium; when there is not equilibrium, very strange things can happen, also because we know much less the laws of chemistry and of physics in such cases.
At equilibrium, pure water becomes solid at =°C = 32°F because the kinetic energy of every molecule has the possibility to being released to the environment, and then the molecule can bind to other molecules forming the crystal of ice.
In a non-equilibrium situation, the molecules don't have such a possibility to immediately release their energy to the environment, so, if they release their energy, they do it to molecules close to them, which then heats up, breaking the bind they could have formed at the beginning. Furthermore, if the water is inside a closed bottle, the improved pressure generated inside from water approaching 0°C, will prevent it to freeze very fast.
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V.Interesting. I must try this.
Many years ago when I first got a computer, one of the things I did was build a temperature probe so that I could record and graph temperature changes. It used a very small bead thermistor and therefore, I hoped, responded much more quickly to changes than a large glass thermometer.
When I used it to plot the cooling curves for water freezing, I got surprisingly varying results: the water appeared to freeze anywhere between 0oC and -8oC (as indicated by the kink in the cooling curve.) This may have been due to instability in my equipment, but it often showed the small rise in temperature, which is characteristic of freezing from a supercooled liquid.
In your example I wonder how much water freezes on shaking? When water freezes, it liberates latent heat of fusion at 334 J/g. This would be absorbed by the surrounding water, heating it by 1oC for each 4.2J/g. So for the entire bottle to freeze to ice at 0oC, the supercooled water would have to start around -80oC. In my freezer I'm lucky to get -15oC, so I wouldn't expect more than about a fifth of the bottle to freeze, before I had a mixture of ice and water at 0oC.(detail below)
When I was puzzling over my results, one of the problems was that I couldn't see what was happening - the surrounding ice/salt mixture obscured it. But if I lifted it out or moved things around to look at the sample, the disturbance would provoke immediate freezing.
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Say 1 litre bottle of water @ -15oC.
Heating that to 0oC takes 1000g x 4.2J/g = 63kJ
That will freeze (63,000J)/(334J/g) = 189g of water ~ about a fifth of the litre.
If your freezer is colder, obviously you freeze more.
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In reply to the query by DonBrown: the bottles were placed in the freezer measured about 100 °F; the temperature in the freezer measures about 28 °F; sometimes a slight touch will cause the water in the bottles to snap freeze while at other times I mush shake the bottles to cause the liquid to change to a solid. It is really cool to see this happen because it takes a few seconds for the bottle to change to a solid. It's like watching a cloud moving down the bottle.
Many years ago, I too, used ratio-metric probes to measure temperature and rainfall to determine when a computer should turn-on electric motors for field crop irrigation. The project was programmed in FORTH. I haven't used that language in many years.
I've been told that the reverse is this super cooling is possible by placing water in a microwave. While the temperature of the water may exceed the boiling point the water may not boil, but when you open the door of the microwave the water may explode.
Someone else told me that each of these experiments is only possible if the vessel is perfectly clean. [???] Is that true?
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I've been told that the reverse is this super cooling is possible by placing water in a microwave. While the temperature of the water may exceed the boiling point the water may not boil, but when you open the door of the microwave the water may explode.
Someone else told me that each of these experiments is only possible if the vessel is perfectly clean. [???] Is that true?
You actually don't need a microwave, even if it's possible that the effect could be more evident. It's common practice in chemistry preparation to boil pure water in clean glass containers, for example flasks, not at a direct flame (to prevent container breakening). In these conditions it's quite usual to have super-heating: water heats up to more than 100°C and a very tiny perturbation, for example just touching the container with something, makes the water boil suddenly and possibly casting almost of them out of the container. For this reason is highly advisable to put fragments of glass or porcelain inside the water, to help it exchange heat in a smooth way. It always works, and it's necessary.
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Doesn't water only freeze at 0°C (-3200°F) at a pressure of 1 bar? Change the pressure and things change. It could be what is happening in the bottles.
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Doesn't water only freeze at 0°C (-3200°F) at a pressure of 1 bar? Change the pressure and things change. It could be what is happening in the bottles.
No, it's much more complicated. What you say is what happens at equilibrium only. In a state of non-equilibrium the behaviour could be completely different, as I wrote up.
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Doesn't water only freeze at 0°C (-3200°F) at a pressure of 1 bar? Change the pressure and things change. It could be what is happening in the bottles.
Water is extremely complicated. It was the pet subject of my PhD supervisor... from memory, at the last count, there were 13 distinct known phases of water (or ice) depending on temperature and pressure (some very high pressures).
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Doesn't water only freeze at 0°C (-3200°F) at a pressure of 1 bar? Change the pressure and things change. It could be what is happening in the bottles.
Water is extremely complicated. It was the pet subject of my PhD supervisor... from memory, at the last count, there were 13 distinct known phases of water (or ice) depending on temperature and pressure (some very high pressures).
Yes, that's absolutely true (but quite the same generally happens for every compound). However it's not this the point. The point relies in the state of non-equilibrium.
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Anyway, the change in water's freezing point with pressure is about a hundredth of a degree for each atmospere of added pressure. The effect would be tiny.
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Do different wavelengths of light, or radio frequencies affect the liquid to ice conversion?
When water converts from a liquid state to a solid state is there any energy release?
Can water be converted form a solid state directly to a gaseous state without first converting to a liquid? Gas to ice?
Water boils faster at altitudes above mean sea level. At what rate, if any, does water freeze faster at altitudes above mean sea level?