Can water be compressed so much that it freezes?

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Intuitively, it makes sense to me that it would. But then again, weird stuff can happen under extreme circumstances...

What would actually happen? Would the temperature of the substance actually increase or decrease under ENORMOUS pressure (i.e., that the molecules could barely move, if possible)?
 

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  • #2
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Yeah, the temperature part of it confused me. I recognize temperature is directly proportional to pressure, but how come the pressure can't be so intense that the molecules are squeezed so tightly that they almost have no kinetic energy?

I understand the equations, but conceptually, I don't.
 
  • #4
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For a substance to be a liquid, its atoms or molecules have to be able to move around each other with ease. The more you compress atoms, the less room they have to move.
 
  • #5
Mapes
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Yeah, the temperature part of it confused me. I recognize temperature is directly proportional to pressure, but how come the pressure can't be so intense that the molecules are squeezed so tightly that they almost have no kinetic energy?
Temperature is only directly proportional to pressure for an ideal gas at constant volume. Depending on the material, a pressure increase can cause an increase or decrease in temperature. Water is one of the materials that gets hotter when pressure is applied, but the increase is much less than directly proportional.
 
  • #6
DaveC426913
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Freezing the water requires that the molecules have a chance to crystalize. Crystalizing requires that the molecules have enough elbow room to do so.

It's not that water wil NOT freeze under extrreme pressure, it's just that water is very complex.

There are actually almost a dozen forms of ice water. Ice I (naturally-formed water-ice) is only one.
 
  • #7
Mapes
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A good rule of thumb is that if any solid phase has a smaller molar volume than the liquid phase(s) (and I don't know of a material where this isn't the case), then the material will freeze under pressure, regardless of temperature. It's the energetically favorable thing to do.
 
  • #8
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To add to what DaveC says, according to this chart, at 300K, or 27C, water is a type 6 solid at 10^9 Pascal pressure.

phase.gif


As you might recall, water expands on freezing. But pressure acts to reduce volume. This is the opposite of what you would want to get it to crystalize in the normal manner. Under higher pressure, at room temperature, water is a different form of solid--whatever type 6, 8 9 and 10 are.
 
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  • #9
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Squeezing something does not necessarily make it change temperature. The solidification of a liquid upon pressure has nothing to do with changes in temperature. It is purely because of the applied pressure.
 
  • #10
DaveC426913
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Squeezing something does not necessarily make it change temperature. The solidification of a liquid upon pressure has nothing to do with changes in temperature. It is purely because of the applied pressure.
Squeezing something does actually change its temp, yes. Look at adiabatic heating, or look at pounding a nail into wood.

But that's not what solidifies a liquid, no.
 
  • #11
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So, we couldn't have oceans deeper than 100 km on Earth because the water at the bottom would freeze under pressure.
 
  • #12
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Squeezing something does actually change its temp, yes. Look at adiabatic heating, or look at pounding a nail into wood.

But that's not what solidifies a liquid, no.
For sure, but the tone of the discussion up until this point had been that some how squeezing it made it colder so it then freezes.

Just to be clear: under pressure, the equilibrium state can change, thus even at the same temperature it is possible to cross phase transitions by applying pressure.
 
  • #13
DaveC426913
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For sure, but the tone of the discussion up until this point had been that some how squeezing it made it colder so it then freezes.
I did not get that impression at all.
 
  • #14
Mapes
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For sure, but the tone of the discussion up until this point had been that some how squeezing it made it colder so it then freezes.
No, I don't agree with this; the Sandia article, for example, mentions that the water heats up to >100°C. Any material that expands with temperature will get hotter upon being pressurized.

Just to be clear: under pressure, the equilibrium state can change, thus even at the same temperature it is possible to cross phase transitions by applying pressure.
I agree with this part.
 
  • #15
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If we look at PV=nRT, as pressure increases so does temperature. So why for water would the temperature decrease upon the addition of pressure.
 
  • #16
Mapes
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If we look at PV=nRT, as pressure increases so does temperature.
PV=nRT is a relationship for ideal gases. We are talking about liquid and solid water.

So why for water would the temperature decrease upon the addition of pressure.
Nobody is saying that it does. We are discussing how solid water can be the stable phase at >0°C when great pressure is applied.
 
  • #17
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dacruick,

If we look at PV=nRT, as pressure increases so does temperature.
This thread is discussing liquid water not water vapor.

For water vapor:

If you compress water vapor to a pressure at or beyond 22.09 MPa the water vapor is considered to be in the supercritical pressure range and the Ideal gas law cannot be used. When you hear of a powerplant operating in the supercritical range that means the boiler is operating at a pressure greater than 22.09 MPa.

Also, for real gases the Ideal gas law should not be used (or be used with caution). You should use a modified version of the Ideal gas law that incorporates the compressibility factor, Z. You could also use a more elaborate equation of state such as, Benedict-Webb-Rubin or Beatie-Bridgeman.

Thanks
Matt
 
  • #18
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If we look at PV=nRT, as pressure increases so does temperature. So why for water would the temperature decrease upon the addition of pressure.
PV=nRT is the ideal gas equation and tells us nothing about phase change. Also, you can have an isothermal process (expansion/compression of a near ideal gas, for instance).

This is an easier phase diagram to understand
http://www.jamstec.go.jp/xbr/2deepstar/02deepenv/figures/page24_blog_entry6_1.png

So the answer is, it depends on what you call freeze and what temperature you're at.
 
  • #19
Mapes
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  • #20
As far as I remember, I was thought once that one caracteristic of fluids is that they are incompressible.

So is that only an idealisation? and they actually can be, given enough pressure? A bit confused here... But maybe its not the same thing and it just means the volume of a fluid cannot ever change?

cheers
Frederic
 
  • #21
Mapes
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It is an idealization made because liquids* are far, far easier to deform by shearing than by compressing. All real materials are compressible to some extent.

*(Note: fluids includes gases, which are relatively easy to compress.)
 
  • #22
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im pretty sure if you look at the triple point chart that chmdude has up it tells all you need to see. increasing the pressure, you cannot make ice. But if you look in the bottom left, apparantly you can increase the pressure of steam to make ice.
 
  • #23
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630px-Carbon_dioxide_pressure-temperature_phase_diagram.svg.png


but here is carbon dioxide and you can increase the pressure of this to phase change it from liquid to solid
 
  • #24
Mapes
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  • #25
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ahh i see, so the chart above just didn't go to a high enough value along the y-axis.?
 

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