Something I've never quite understood, or was told the answer and subsequently forgot:
Why does water expand when frozen?
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boredrich
- 2008-06-25 @ 08:11:39
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DominicGee
- 2008-06-25 @ 08:53:55
Well, every other fluid contracts when frozen - this makes perfect sense in terms of the chemistry I was taught. But water, against all expectation expands when it should contract. Why? WHy?
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SeasideMan
Pro - 2008-06-25 @ 08:57:02
It's the weak hydrogen bonds in the water. The hydrogen atom from one molecule forms a weak attraction with the oxygen atom of another molecule. These bonds get stronger as water cools, because there is less heat energy to cause the molecules to move about. The result in ice is a crystal structure with gaps in it, which is slightly less dense than liquid water. About 9% less dense in fact.
Water is at it's most dense at 4C, which is why that is the temperature at the bottom of most deep oceans. It's a good job water behaves like this, otherwise ponds would freeze solid in winter and kill everything living in it.
Tom.-
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DominicGee
- 2008-06-25 @ 09:00:42
Thank you... water is an odd substance isn't it. We take it for granted now, but chemically it seems to have many properties not shared by other liquids.
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grumpus
Pro - http://bobmblack.blog.co.uk
- 2008-06-25 @ 11:47:39
Also the fact that ice (frozen water) is less dense than the water itself, is what makes it float. This raises other questions in my mind:
1) Are ice and water two different substances?
and if not
2) Is water the only substance that floats on itself? -
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SeasideMan
Pro
- 2008-06-25 @ 12:53:37
Ice and water are just water at different temperatures, and steam is the 3rd one. They aren't allotropes like diamond and graphite are of carbon, just the same substance at a different temperature.
I'd be surprised if water was the only substance in which the solid is less dense than the liquid form, but offhand I don't know of any others.
Carbon dioxide is interesting in that it has no liquid state: it turns directly from solid into gas when heated from the solid state.
Tom.-
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grumpus
Pro
- http://bobmblack.blog.co.uk
- 2008-06-25 @ 15:10:15
I bow to your amazing knowledge.
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SeasideMan
Pro
- 2008-06-25 @ 15:12:46
I just have a reasonably good memory - that was just O-level physics and chemistry!
Tom. -
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erm I think it has something to do with molecules being more compacted together and joining together I cant quite remember its been a long time since I left school