Supercool

Most recent answer: 03/23/2008

Q:
Last weekend my family and I took a trip to the Rocky Mountains. During our travels, we took bottled water with us. Unfortunately, I discovered that I left three bottles of the water in my car overnight where the temperature dipped to 4 degrees Fahrenheit. When I went to load my car in the morning, I noticed the water and thought it would be frozen. When I looked at the bottles they looked as if they were normal, however when I picked one of the bottles up it froze before my eyes. I thought it was a bit unusual so I tried it to the other two bottles and the same thing happened. Please explain how the water went from the liquid state to a frozen state before my eyes (It was cool!).
- John (age 47)
Greeley, Colorado
A:
John- This is the sort of thing which is hard to get to happen when you try to do it in front of a class. Then somebody like you gets lucky.

 Liquids can be 'supercooled',  which means cooled to below their freezing point. However, they don't actually freeze until some disturbance (maybe a piece of dirt, or a mechanical shake) accidentally gets a little bit of ice started.
There's one thing that doesn't quite make sense. When water turns to ice it releases 334 J of heat per gram. That's enough to heat about 5 grams of water by 28 °F, enough to raise the temperature of your 4°F water to the melting point. So for every gram that freezes when you shake the bottle, I'd expect about 5 grams to stay liquid. is it possible that the 'frozen state' you found was actually a sort of slush- part ice, part liquid?

Mike W.

(published on 03/23/2008)