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Warm water expands?

  1. Apr 13, 2006 #1
    In a Time article about global warming they say warm water expands, but water expands when it's frozen - is it both ways 'round?
  2. jcsd
  3. Apr 13, 2006 #2


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    Yes, warm water expands, just like warming anything.

    And, as you cool water, it contracts- until it starts to freeze- then, because it forms rather large crystals it suddenly expands (have you ever stopped to think how much of life depends on that fact?). If you continue to cool ice after it has completely frozen, it will contract again.
  4. Apr 13, 2006 #3

    Doc Al

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    Pure water has its maximum density at about 4 degrees C.
  5. Apr 13, 2006 #4
    I've read that water is quite an odd substance in that it expands when it freezes. Is this true, and is this thing to expand at two (or more) far-apart levels of temperature also odd?
  6. Apr 13, 2006 #5


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    Yes and yes. And extremely fortunate for life as we know it, as HallsofIvy alludes to.

    It has to do with the polar nature of water - one end of the molecule is positively charged, the other is negatively charged. When they get clsoe together and start to line up (i.e. crystalize), they don't line up in the most compact pattern, they line up according to their charge attractions, which takes up more room. This results in water taking up *more* room as it crystalizes, rather than less as with most other molecules and elements.
  7. Apr 13, 2006 #6


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    Yes and yes. And extremely fortunate for life as we know it, as HallsofIvy alludes to.

    And because it is both unique and highly beneficial to life, this is a very compelling reason why extra-terrestrial life is very likely to be water-based.
  8. Apr 13, 2006 #7
    Are there any other similar substances to water with similar properities?
  9. Apr 13, 2006 #8
    Just to add on what's already been said, why is water so essential to life? Well if it didn't expand when it was frozen then its density would not decrease. I'm sure everyone is familiar with ice cubes that are less dense then water floating on the surface. If ice did not do not then there would be an awful positive feedback loop that would freeze more of the world's ocean waters. The frozen water on hte surface is able to be heated by the sun's radiation, but if were not able to float it would sink to the bottom.
  10. Jan 28, 2007 #9
    second party interested...

    Hello, I'm also very interested to know if there are any other substances that expand, albeit over a narrow (yet life-preserving) temperature range.
  11. Jan 29, 2007 #10


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    There are several materials with a negative coefficient of expansion (Google: negative CTE). Many composites and fibers (eg: kevlar) exhibit at least one axis with negative CTE. Polymers like HDPE exhibit negative CTE over small temperature ranges. But probably the most widely studied materials are the oxides (including many silicates and related zeolites), following the discovery of uniform negative CTE in zirconium tungstate (and subsequently in related oxides).

    With polymers, the negative CTE usually from thermally breaking cross-linkages between chains. In the oxides, the culprit is usually the rotational modes of the M--O--M bonds.
    Last edited: Jan 29, 2007
  12. Jan 29, 2007 #11
    expressed gratitude

    many thanks
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