Why triple point of water is higher than freezing point

In summary, water can exist in a liquid and a solid state at the triple point, which is above 0 Celsius.
  • #1
animalcroc
59
0
Why is the triple point of water .01C while the freezing point 0C? It seems contradictory.
 
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  • #2
The opposite would be more surprising to me. Why does it feel contradictory to you?
 
  • #3
Water, bismuth, and a very small number of other substances, have the rare distinction of possessing a melting curve with a negative slope.
 
  • #4
cesiumfrog said:
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
animalcroc said:
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
animalcroc said:
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
cesiumfrog said:
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
Claude Bile said:
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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1. What is the triple point of water?

The triple point of water is the temperature and pressure at which all three phases of water (solid, liquid, and gas) coexist in equilibrium.

2. How is the triple point of water determined?

The triple point of water is determined by measuring the temperature and pressure at which the solid, liquid, and gas phases of water are in equilibrium. This can be achieved by using a device called a triple point cell.

3. Why is the triple point of water higher than the freezing point?

The triple point of water is higher than the freezing point because it is the temperature at which all three phases of water coexist in equilibrium. This requires a specific combination of temperature and pressure, which is higher than the standard freezing point of water at 0°C and 1 atmosphere of pressure.

4. What factors affect the triple point of water?

The triple point of water is affected by pressure, which can change the temperature at which water transitions between its phases. It is also affected by impurities in the water, which can shift the triple point to a slightly higher or lower temperature.

5. Why is the triple point of water important?

The triple point of water is important for a variety of scientific and practical reasons. It is used as a reference point for temperature and pressure measurements, and it is also crucial for understanding phase transitions and the properties of water. It also has practical applications in industries such as food preservation and climate control.

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