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Why triple point of water is higher than freezing point

  1. Oct 22, 2007 #1
    Why is the triple point of water .01C while the freezing point 0C? It seems contradictory.
     
  2. jcsd
  3. Oct 22, 2007 #2
    The opposite would be more surprising to me. Why does it feel contradictory to you?
     
  4. Oct 22, 2007 #3

    Gokul43201

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    Water, bismuth, and a very small number of other substances, have the rare distinction of possessing a melting curve with a negative slope.
     
  5. Oct 23, 2007 #4
    Liquid water at atmospheric pressure cannot become ice until it cools to 0 C, by the definition of freezing point. So, how can ice exist at the Triple Point (above 0 C) since it has not yet reached 0 C ?

    It seems that the Triple Point should be 0 C, not 0.01 C.
     
  6. Oct 23, 2007 #5

    Claude Bile

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    The triple point of water is not at atmospheric pressure.

    Claude.
     
  7. Oct 23, 2007 #6
    Since water normally boils at 100C, shouldn't you naively expect (based on your above argument) that the triple point (where steam and ice coexist) must be somewhere between 0C and 100C, rather than at either extreme. (Of course, normal experience isn't very helpful in extrapolating to abnormal domains..)
     
    Last edited: Oct 23, 2007
  8. Oct 24, 2007 #7

    Gokul43201

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    You'd have to be really naive! You'd be wrong if you made this kind of guess with most any other liquid.
     
  9. Oct 24, 2007 #8
    The answer I was seeking! Where the hell did I come to believe that the TP was at 1 atm? Oh well.
     
    Last edited: Oct 24, 2007
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