Water needs air to freeze?

cobb

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I have my freezer full of deer park water bottles and use one for my neck for mild pain relief. ANyway, I unscrewed the lid to let some air out as the bottle looked like it was about to explode. Later on I accidently unscrewed the lid with it under a shoulder and some air and water came out. I screwed the lid back on right and pulled it out.

After being in the freezer for 2 days, it was still liquid and the bottle looked crushed. I unscrewed the top a bit to let in some air and it seemed to instantly freeze. Later on I checked on it and it was rock solid, but the water or ice was clearer than the other bottles.

Just wondering.......
 

Empath

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Water freezes at 0C or 32F at normal atmospheric pressure. It doesn't require air to freeze, but the atmospheric pressure plays a physical role in the change of state. Freezing point is higher under higher pressures, and lower under lower pressures.

The crushed look from your bottle in the freezer was due to the air in the bottle contracting at the low temperatures, creating an even greater vacuum. The water too contracts at lower temperatures, until it reaches the freezing point and then expands. The low pressure in the bottle may have lowered the freezing point of the water to even lower than the temperature of your freezer. When you opened the cap, the air pressure equalized with the atmospheric pressure and restored the freezing point to 32 degrees. Considering the temperature of the water, it should freeze nearly instantly.

Incidentally, if you were keenly aware of everything occurring, you would noticed that the bottle temperature raised just a bit while it froze. That's because the water, when it changed to a solid state, gave off 80 calories of heat for every gram of water in it.
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Edit: *Warning* consider the remarks regarding pressure in this posting unsupported and unreliable. Actually, consider the comments as backward. For the sake of continuity with the follow-up commentary and worthwhile opposing viewpoints, I've left the comments intact.
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BB

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Water, whether freezing or boiling, usually needs some sort of "seed" to start the process.

If you have filtered water and a smooth container, you can have either super heated liquid (above boiling) or super cooled liquid (below freezing).

There are other chemicals that are more prone to this than water (remember in chemistry class you had to have a glass rod or marbles in the bottom of a beaker before "boiling" a liquid.

With water, it is rare to see it happen--I have seen it a few times with bottled water in a home freezer (it is "cool" to watch a bottle of water freeze solid in just a few seconds after you give it a shake), or in a microwave if you have ever boiled some hot water in a glass container only to hear a "pop" and find much of the water blown out of the cup.

The point at which the phase change is initiated is called the "nucleation site"... (IIRC).

Regarding the bottle looking crushed--if you have been freezing and thawing the same bottle--the plastic will be stretched when the water freezes and when the water thaws (or is super cooled) the volume of the water will be roughly 7% (IIRC) less than the ice was--forming a partial vacuum in the now oversized bottle.

-Bill
 

evan9162

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I've supercooled water in a shot glass before. I used a peltier to cool the water down, it got to about -5C, then by tapping the glass with the thermocouple probe I had in the glass, I was able to form a nucleation site, causing instant solidification of much of the water. The neat thing was, that the remaining liquid water ended up at about 3 or 4C immediatley afterwords. The solidifying water dumped the excess energy from the phase change into the surrounding water, warming it up.
 

Sub_Umbra

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[ QUOTE ]

Water freezes at 0C or 32F at normal atmospheric pressure. It doesn't require air to freeze, but the atmospheric pressure plays a physical role in the change of state. Freezing point is higher under higher pressures, and lower under lower pressures.

[/ QUOTE ]

Emphasis mine.

Wouldn't the opposite be true? Have you ever placed a warm soda (mostly water) into the freezer after bringing it home from the store? If you leave it in the freezer just a little too long to chill it, it looks just fine (still liquid) as long as the cap still is on (under higher pressure than one atmosphere). When the cap is removed and the contents drop to a lower pressure it slushes up or freezes up instantly.

That would indicate that greater atmospheric pressure LOWERS the freezing point of water.
 

js

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I'm pretty sure that the supercooling phenomenon can account for some, all, or more than all, of the energy of fusion (80cal/g), so that it is possible for the water to solidify very quickly and NOT pull ANY heat from its' surrounding, or even end up at less than 0 C. Otherwise, you would end up with some contradictions, thermodynamically speaking, because it takes energy to supercool a liquid. i.e. you must remove more heat from it than you would need to merely to bring it to the freezing point.
 

binky

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In the phase diagram here at Encarta you can see that for a given temp (say, just below zero C) increasing the pressure will return the frozen phase to liquid, and lowering the pressure will return it back to solid.

So... (within that range below the triple-point on the diagram) LOWER => solid, HIGHER => liquid
And... freezing point occurs at a LOWER temp under higher pressure, and HIGHER under lower pressure.
 

js

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Sub,

Yeah, I was just mentally thinking through that same thing, and wishing that I had my thermodynamic text book from college. Then I realized I DO HAVE MY THERMO BOOK. I was psyched! Ran to my office, opened it up, and checked.

Yes. For a pure substance that expands upon freezing, the solid-liquid interface line has a negative slope on the pressure vs. temperature line. So yes, at higher pressures, the freezing temperature is lower.

However, it's just a bit more involved than that, because that graph is assuming that the volume can be whatever it needs to be. But if you restrict the volume in one or more dimensions, that changes things, I think (but I'm not sure.) In other words I think that if you prevent water from being able to expand (which takes ENORMOUS FORCE) that you will supercool it.

But certainly, if you exert pressure on a volume of water via the air, for example, then yes, water freezes at a slightly higher temperature in Denver, than in Boston.

Also, as you point out, keeping the temperature fixed, it is possible to go from high pressure to low, and cross the solid-liquid line, thus causing the soda to turn to slush.

And then there's the triple point, but I remember that that thing gave me a head ache when I took thermo, so I'll let that be. But it's a neato idea. There is only one point on the pressure-temperature graph where solid, liquid, and gaseous H2O can all co-exist. But, it's specific volume would depend on the exact ratios of those things. i.e. it's possible to have varying amounts of ice, water and gas for the same initial mass of water.
 

js

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[ QUOTE ]
binky said:
In the <url="http://encarta.msn.com/media_461541579/Phase_Diagram_for_Water.html">phase diagram here at Encarta</url> you can see that for a given temp (say, just below zero C) increasing the pressure will return the frozen phase to liquid, and lowering the pressure will return it back to solid.

So... (within that range below the triple-point on the diagram) LOWER => solid, HIGHER => liquid
And... freezing point occurs at a LOWER temp under higher pressure, and HIGHER under lower pressure.

[/ QUOTE ]

You MUST be ABOVE the triple-point to be at the solid-liquid phase line.
 

BB

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Without referring to a my 30 year old chemistry book... The amount of heat released taking water from 100C to 0C is approximately the same amount as the energy released at taking water from liquid to solid at 0C.

So, what Evan observed is really more to the point--when I saw the water "flash freeze"--the ice was probably forming down the walls of the bottle and left a core of unfrozen water--that had been warmed by the act of crystallization.

I don't believe that there is any substantial energy difference between cooling water from 5C to 0C as there is super cooling water from 0C to -5C... The massive energy release is the act of crystallization itself.

Regarding the change in water freezing point would require larger changes in pressure I believe than the few PSI or tens of PSI possible in a water bottle.

Here is a quick link on water freezing...

Water Freezing Properties under High Pressure

To drop the freezing point of water to ~-22C, you would need to pressurize it to approximately 2.7kBars (roughly 40,000 PSI)... More info on the link.

I have to go now... Bye!

-Bill
 

binky

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[ QUOTE ]
js said:
[ QUOTE ]
binky said:
In the phase diagram here at Encarta you can see that for a given temp (say, just below zero C) increasing the pressure will return the frozen phase to liquid, and lowering the pressure will return it back to solid.

So... (within that range below the triple-point on the diagram) LOWER => solid, HIGHER => liquid
And... freezing point occurs at a LOWER temp under higher pressure, and HIGHER under lower pressure.

[/ QUOTE ]

You MUST be ABOVE the triple-point to be at the solid-liquid phase line.

[/ QUOTE ]

I was actually referring to temp there. Really. What I meant was that if you choose some given temp in that range below the triple-point, and you travel LOWER & HIGHER in pressure... etc.
That's honestly what I meant. You gotta be BELOW the triple-point on temp to get any solidification. We're saying the same thing. Sorry for the mixup.
 

Sub_Umbra

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Jim,

Thanks for the explanation. After my first post I Googled around a bit and became really confused. Funny you should mention a headache. This is way too much for me. I'm really just the guy trying to get his Diet DR Pepper cold without having the slush come out when I open it.

Sub
 

McGizmo

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I recall reading that in one of the first deep sea labs, one of the researchers brewed some instant coffee (they were under pressure; above 1 atm) and proceeded to burn his mouth and throat rather severly. The water was considerably hotter than normal when it came to a boil. /ubbthreads/images/graemlins/icon15.gif
 

BB

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Brock, I am confused... You said that sea water can be at -5ºF at 5,000' because of the temperature… I don't think so. It could only be at this state because of super cooling of the sea water, not because of the salt content or the lower atmospheric pressure.

Sea water begins to freeze about -2ºC (~29ºF). An Eutectic (sodium chloride) Brine solution freezes at -6ºF (-34ºC). And from the table I posted earlier freezing point of fresh water decreases with increased pressure "by about 0.55ºC per 80 atmospheres of pressure down to about -22ºC at 2,700 atmospheres of pressure"... And you can super cool fresh water down to about -42ºC (about -43ºF). And even a NaCl brine solution—if I read the research correctly it shows that you can get a super cooled liquid down to the -45C range.

The links below correspond to the point, in order, made above:

Properties of Sea Water
Salt Brine for Fishing Industry
High Pressure Cryonics
Amorphous Ice and Glassy Water
Super Cooled Brine Solution (pdf)

And in your example you are lessening the pressure by less than 0.25 Bar (a Bar is 1 atmosphere which is roughly 14.7 PSI at sea level--IIRC)--which, if anything should cause the ice to form at a, very slightly, warmer temperature at 5,000 feet. But absent super cooling, sea water should begin freezing around 29ºF and probably freeze solid by around -6ºF (assuming the brine becomes more and more concentrated—if that is even a possibility).

Am I missing something?

-Bill
 

BB

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"pure water ice in space"... Well you can place an ice cube in space from a space ship--but it will probably evaporate within a few minutes to a few hours (to sublime is to change from solid to gaseous state without melting) if it is anywhere near earth/solar system.

Will you find "pure water" in space? Probably not pure in the sense you could drink it.

There are instances of, what is believed to be water ice,
<ul type="square">[*] at the poles of the Moon in deep craters protected from the sun, [*]possibly on Mars and moons around outer planets with atmospheres, [*]and comets are believed to be "dirty snowballs" and the trail you see is the solar wind blowing the melting gases from the head of the comet as it comes closer and closer to the sun.[/list]

Is this kind of what you were asking Green?

-Bill
 

mattheww50

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Actually the most likely explanation is one long understood.
Presence of any dissolved substance in water depresses the freezing point, about 2 degrees per mole of solute/liter. However some molecules disassociate in water, so for instance 1 mole of salt (NaCl) will depress the freezing point more than 2 degrees because you end up with roughly a mole of sodium and roughly 1 mole of Chlorine.


Also keep in mind that while the solubility of solids decr eases with decreasing water temperature, the solubility of gases INCREASES. There is usually considerable air dissolved in tape water (by design). The reason the ice cubes you make are not clear, is the air is forced out of solution as it freezes. If you want clear ice cubes, boil the water first to drive the dissolved air out, or thaw and refreeze the ice.

Many is the can of soda I have taken out of the freeze, and watched it promptly freeze after I opened it.
opening it allowed the gas (carbon dioxide to come out of solution), so it was suddenly below the freezing point, and promptly turned to slush..
 
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