Supercooled water in the freezer

Q:I put a bottle of water in the freezer every night before bed. In the morning, I take it out and drink it. Sometimes its frozen solid, sometimes it stays liquid, depending on when I put it in there. But here’s the kicker, sometimes I will pull the bottle out, it will be liquid, but as soon as I open it, it starts to turn into ice, from the top down (it takes a few seconds for the entire bottle to freeze. Is there an explanation for this?

-Greg (age 26)
Army, Iraq
A:We suspect that what’s happening here is that the water in the bottles which did not freeze overnight was "supercooled." Water normally freezes when it is cooled below 0 degrees Celsius, forming ice crystals. Ice crystals form more easily when they grow on existing ice crystals -- the water molecules like to pack themselves in place on a crystal that’s already gotten started. It doesn’t take much to start the crystallization process going -- a little piece of dust or other impurity in the water, or even a scratch on the bottle are sometimes all it takes to get ice crystals growing. The process of starting off a crystal is called "nucleation."

In the absence of impurities in the water and imperfections in the bottle, the water can get "stuck" in its liquid state as it cools off, even below its freezing point. We say this supercooled state is "metastable." The water will stay liquid until something comes along to nucleate crystal growth. A speck of dust, or a flake of frost from the screw-cap falling into the bottle are enough to get the freezing going, and the crystals will build on each other and spread through the water in the bottle.

Water releases 80 calories per gram when turning from a liquid to a solid. We suspect your freezer is only a few degrees Celsius below zero(perhaps ten or fifteen?), and the specific heat of water is one calorie per degree per gram. This means that your water, as it freezes, warms up the rest of the water until the process stops at 0 degrees Celsius, freezing perhaps ten or twenty percent of the water. This ice may be distributed throughout the bottle, though, as the crystallization process happens very quickly and heat flows slowly.

We suspect you have slush in your bottle rather than hard ice when this is done. You can compare with another bottle which froze hard in your freezer overnight how hard it is to squeeze the bottle and how long it takes to melt. The ice will also take up more room than the water it used to be, and some water may spill out the top.

There can also be some small effects of pressure and of dissolved gases on the freezing temperature. Is your water under pressure?

Tom and Mike

(republished on 07/25/06)

Follow-Up #1

Q:Water in my mom’s freezer or fridge,doesn’t matter which one, can be in there for days and it won’t freeze solid. In fact it looks perfectly clear until you do one of 3 things. You shake it, you drop it or you open it. It then turns to slush. I want to do a science fair project on this because it’s amazing to me, but I’m not sure what my hypothesize would be. I was thinking that maybe oxygen had to be present to freeze, but you are saying that it all begins just with the change that causes the cystals to grow?

-Jordan Canevari 11
Okeechobee,Florida, usa
A: Right. You’ve actually done the experiment to show that oxygen is not the key. Shaking or dropping the bottle doesn’t add oxygen to it, but does trigger the slush formation.

Mike W.

(published on 11/10/06)

Follow-Up #2

Q:How super cooled can water get without freezing? also i would just like to comment that i was searching for this answer because the same thing was happening to me here in iraq.

-Greg (age 24)
Navy, Iraq
A:According to Wikipedia http://en.wikipedia.org/wiki/Supercooled water can be supercooled to a little below -40°C, at least briefly. I suspect that in practice it will be hard to go below about -20°C, just because ordinary bottles, bubbles, dust, etc. can nucleate freezing. The number of people who have written about observing this is now pretty large, so it seems easier to get large supercooling than I'd guessed.

Mike W.

(published on 07/03/08)

Follow-Up #3

Q:Thanks for the explanation! I observed this for the first time the other day, then reproduced it just to make sure it wasn't a fluke. Amazing and perplexing to watch the first time.

-Eric Ford (age 37)
Mesa, Arizona, USA
A:Thanks for the info,

(published on 08/23/09)

Follow-Up #4

Q:How is the freezing temperature of water affected by pressure? This phenomenon happened to me as well but I assumed supercooling was caused by the water in my water bottle being under a slight vacuum (the bottle was 'sucked in' when I put it in the freezer) and when I opened it the pressure change to atmospheric caused the phase change. Surprisingly I could not find a lot of data on the internet about this. My thermodynamic book has many property tables on superheated water vapor but little to say on the solid-liquid properties of water.

-garrett (age 26)
houston, tx
A:Liquid water and ice have only slightly different volumes, so the freezing point isn't very sensitive to pressure. To the extent that it is, higher pressure favors the liquid, which (somewhat unusually) has smaller volume. Since your bottle's pressure seemed to slightly rise when opened, that effect would actually tend to reduce freezing. However, it's a very small effect and in this case is swamped by the nucleation phenomenon.

Mike W.

(published on 08/23/09)

Follow-Up #5

Q:I also put my water bottle at work in the freezer occasionally to cool the water faster to drink. The "supercooled water" happened to me today too. I took the water out and walked back to my desk. The water was completely clear and did not look frozen at all, but I noticed small bubbles floating through the water much more slowly than normal. When I opened the bottle to take a drink at my desk, it pretty quickly became opaque and started freezing. Needless to say I was amazed. Before the supercooled water freezes, does is it somehow thicker or denser than normal water? The bubbles floating very slowly was really weird.

-David (age 29)
Laguna Niguel, CA
A:This sounds like a really interesting observation. I'm posting it just to see if anybody has any thoughts.

It's just possible that the bubbles themselves started nucleating some freezing, so perhaps they were dragging little ice crystals along, but that's just a wild guess.

Mike W.

(published on 08/23/09)

Follow-Up #6

Q:FYI the bottled water provided to troops in Iraq is produced from Kuwaiti desalinization plants. Not from ground water as is common in the US. Might the desalinization process produce unusually pure water with no dissolved salts or mineral which is therefore be prone to super cooling?

-Evan (age 34)
previously Kuwait
A: Yes, it's possible that the desalinated water lacks nuclei. For example, if it's prepared by reverse osmosis, that could filter out various impurity nuclei.
Thanks for the interesting info.

Mike W.

(published on 08/23/09)

Follow-Up #7

Q:when at work i commonly place a 2-liter of room temp soda in the freezer at 2 hours 15 minutes when i come to break its liquid(rarely partly frozen but it does happen) when opened it turns to a delicious slush. wouldn't the impurity's in soda prevent a supercooled state.

-Jason (age 23)
florida
A:Not necessarily. The sugar and flavorings are individual smallish molecules. The nuclei which start the freezing are larger particles, such as specks of dust.

Mike W.

(published on 11/04/09)

Follow-Up #8

Q:The same thing happened to me on MULTIPLE occasions and here is the kicker...It also happened in Iraq. Mosul Iraq to be more clear and we had a freezer full of water bottles. Pull one out and hit the tabl with it and it woukd fkash freeze ,Take another out and repeat. Opening the bottle, smacking it, shaking it..all these things would initiate the flash freeze. Ive never seen it happen stateside, only at a couple locations in iraq during 06,07.

-Matthew O''Farrell (age 26)
El Paso. TX
A:I'm starting to strongly suspect that the bottled water supplied in Iraq was prepared by reverse osmosis, and that many of the little nuclei usually present were filtered out in the process.

Mike W.

(published on 11/04/09)

Follow-Up #9

Q:Not a question, just an observation that this doen't just happen to small bottles. I had a 5 gallon bottle of water sitting on the porch last winter. I walked past it and wondered why it hadn't frozen, even though the temperature had dropped well below freezing over night. I thought maybe it had but I just wasn't able to tell, so I grabbed the bottle neck and tilted it and at that point I could see the ice form from top to bottom. It became opaque, as the ice was slushy.

-Craig (age 60)
Greenville, NC, USA
A:Good new data point.

Mike W.

(published on 11/05/09)

Follow-Up #10

Q:I've seen this several times. I live in northern Illinois, and our winters get a lot of cold draft out of Canada/Minnesota. I commonly leave filtered water in bottles on my deck to stay cold for the next day during the winter. Several things I've observed: Water purity is the #1 important factor to see this. Reverse osmosis = supercooled. Brita/Pur filtered = frozen. Container cleanliness is 2nd. Fresh from the bottling plant = supercooled. Reused/recycled plastic = frozen. Lastly, in order to start the freezing process, I've often noticed that only motion is needed. I think of it as motion allowing the water molecules to "realign" themselves, thus, allowing them to start forming ice crystals around whatever they want to. I've grabbed one on my way out to the car and observed it go from water to solid ice in the 6 second walk. I've also seen quite a bit of the slushy. Ambient tempurature is important in deciding this one, the colder, the slushier. As the water forms crystals, it warms up, and when in a sealed container, pressure builds as well (water expands when frozen). Boyle's Law plays on this one, helping to increase the temp, as well (as pressure goes up, so does the tempurature). At the very least, it's a cool parlor trick. "Hey, go grab me a bottle of water, they're on the porch." "Aren't they frozen?" "Nope." (from the porch) "WHOA!" (back in the house) "Hey, this was water out there." "Dude, it's -10° outside...are you nuts?"

-Dan (age 24)
Rockford, IL, USA
A:Thanks, those are great data! It all fits with the idea of needing some special nuclei (usually bits of dust, etc.) to start the freezing.

On the theory issues: The water molecules are moving around very quickly on their own even before you pick up the bottle, thanks to thermal energy. However, they do so without any collective structure large enough to start the freezing. When you pick up the bottle, some larger scale disturbance (e.g. a small bubble) is introduced, and that can be enough to nucleate the ice.

Mike W.

(published on 11/12/09)

 

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