Why triple point of water is higher than freezing point

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  • #1
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Why is the triple point of water .01C while the freezing point 0C? It seems contradictory.
 

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  • #2
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The opposite would be more surprising to me. Why does it feel contradictory to you?
 
  • #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.
 
  • #4
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The opposite would be more surprising to me. Why does it feel contradictory to you?

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.
 
  • #5
Claude Bile
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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 ?
The triple point of water is not at atmospheric pressure.

Claude.
 
  • #6
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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 ?

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..)
 
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  • #7
Gokul43201
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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.
You'd have to be really naive! You'd be wrong if you made this kind of guess with most any other liquid.
 
  • #8
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The triple point of water is not at atmospheric pressure.

Claude.

The answer I was seeking! Where the hell did I come to believe that the TP was at 1 atm? Oh well.
 
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