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  #1  
Old 10-22-2004, 12:03 PM
Jinx Jinx is offline
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What Temp Does Water Freeze, in Denver?

I know it sounds like there's a trick to this question, but I was just wondering: At what temp does water freeze at a high altitude? Does lower air pressure change the freezing point at all? - Jinx
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  #2  
Old 10-22-2004, 12:21 PM
bashere bashere is offline
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Quote:
Originally Posted by Jinx
I know it sounds like there's a trick to this question, but I was just wondering: At what temp does water freeze at a high altitude? Does lower air pressure change the freezing point at all? - Jinx
Changing the pressure does change the freezing point, but it is not as volatile as the boiling point of water is. This site:

http://www.lsbu.ac.uk/water/phase.html

has a phase diagram (look for the big phase diagram) that includes the change in freezing point. Denver (assuming it really is the "mile high city") has a pressure of roughly 63,000 Pa. The change in the freezing point occurs at roughly 1000 Pa, or (if I am doing the math correctly) 121,800 ft above sea level; about 22 miles up.

I'm really only familiar with this going the other direction; that is, when calculating the change in boiling temperature due to changes in pressure. I found this cite helpful as well:

http://hyperphysics.phy-astr.gsu.edu...ic/vappre.html

A real chemist of physicist should be along shortly to correct my misunderstandings.
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Old 10-22-2004, 12:22 PM
friedo friedo is online now
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Indeed, it does. Air pressure and water freezing.
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Old 10-22-2004, 12:39 PM
bashere bashere is offline
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Sorry, I did that wrong. One of my sites gives changes in mmHg, the other gives it in Pa's. The correct conversion is 1 mmHg = 133 Pa, not 1 = 100 like I thought. This gives the point at which the freezing point of water changes (according to the phase diagram) at closer to 7.5 mmHg, or about 130,000 ft, or call it close to 25 miles up. Note that at that point, water doesn't have a "liquid" state; your choices are frozen or vapor.

Again, check my math before moving to Denver.
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Old 10-22-2004, 05:40 PM
David Simmons David Simmons is offline
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According to my Hausman and Slack Physics book, at temperatures found in the atmosphere\surface interface a pressure increase of 100 atmospheres lowers the freezing point less than 1 Celcius degree.
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Old 10-23-2004, 10:28 AM
Crafter_Man Crafter_Man is offline
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This is one of the reasons the melting point of water (0 C) is no longer used as a defining/fixed point in the temperature scale. It was replaced by the triple point of water (0.01 C) in 1948.
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  #7  
Old 10-23-2004, 10:45 AM
WhyNot WhyNot is offline
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Um, so (at) what temperature does water freeze in Denver?
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Old 10-23-2004, 11:49 AM
Polycarp Polycarp is offline
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Quote:
Originally Posted by bashere
Sorry, I did that wrong. One of my sites gives changes in mmHg, the other gives it in Pa's. The correct conversion is 1 mmHg = 133 Pa, not 1 = 100 like I thought. This gives the point at which the freezing point of water changes (according to the phase diagram) at closer to 7.5 mmHg, or about 130,000 ft, or call it close to 25 miles up. Note that at that point, water doesn't have a "liquid" state; your choices are frozen or vapor.

Again, check my math before moving to Denver.
Moving directly from solid to gaseous state is sublimation, and occurs even at normal lowland air pressure with water in dry, cool weather -- the morning sun on a thin icy coating, with a very low humidity, will cause it not to melt but to turn directly to water vapor. It's why liquid carbon dioxide occurs on earth only in high-pressure laboratories -- the "liquefaction pressure" is something like 20 atmospheres.

I'd have to have one of our resident planetologists discuss this in more detail, but as I recall, the only known place off Earth where liquid water can exist under "natural" conditions (though owing to lack of atmospheric water vapor it won't) is the Hellas basin on Mars, where the air pressure is -- barely -- high enough and the temperature at local summer noon is sufficient, for liquid water to be present. (But the effectively 0% humidity of the Martian atmosphere would mean it would quickly vaporize.)
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Old 10-23-2004, 02:24 PM
Ponder Stibbons Ponder Stibbons is offline
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Quote:
Originally Posted by WhyNot
Um, so (at) what temperature does water freeze in Denver?
Looks like we'll never know.

I'm too lazy to work out the math, plus I'm not too good at math to begin with.
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Old 10-23-2004, 02:48 PM
bashere bashere is offline
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Originally Posted by Ponder Stibbons
Looks like we'll never know.

I'm too lazy to work out the math, plus I'm not too good at math to begin with.
Wow, I actually left that part out. 0.01C. Under all of the normally-occuring pressures on the surface of the planet, the freezing point of water is roughly 0.01C. At REALLY extreme ranges (e.g. 25 miles above sea level) it changes.
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Old 10-23-2004, 04:26 PM
Ignatz Ignatz is offline
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So, for those who aren't into metrics and still use U.S. Standards and as f = 9/5 x C + 32, then it freezes at about 32.018 degrees F, I think.
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Old 10-24-2004, 05:15 PM
Chronos Chronos is offline
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Quote:
I'd have to have one of our resident planetologists discuss this in more detail, but as I recall, the only known place off Earth where liquid water can exist under "natural" conditions (though owing to lack of atmospheric water vapor it won't) is the Hellas basin on Mars
It may be possible there; I can't speak to that. But it's not the only place. There's almost certainly liquid water beneath the ice on Jupiter's moon Europa, and I wouldn't be surprised to find it in/on any of the other gas giant moons, either. It might even be possible to have liquid water deep inside the gas giants themselves.
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Old 10-24-2004, 09:40 PM
LSLGuy LSLGuy is offline
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Quote:
Originally Posted by Ignatz
So, for those who aren't into metrics and still use U.S. Standards and as f = 9/5 x C + 32, then it freezes at about 32.018 degrees F, I think.
What bashere means is that water freezes at 0.01C ~= 32.018F at sea level, down in Death Valley, and up at Denver, and on Mount Everest, and even up to 120,000+ feet above sea level.

Only above there, as the air pressure starts to fall of towards that of a decent vauum, do you begin to see even minimal changes in the freezing temperature of water.
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Old 10-24-2004, 10:34 PM
David Simmons David Simmons is offline
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Quote:
Originally Posted by LSLGuy
What bashere means is that water freezes at 0.01C ~= 32.018F at sea level, down in Death Valley, and up at Denver, and on Mount Everest, and even up to 120,000+ feet above sea level.

Only above there, as the air pressure starts to fall of towards that of a decent vauum, do you begin to see even minimal changes in the freezing temperature of water.
And maybe down in the oceanic abyss where pressures can reach 1000 atmospheres.
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  #15  
Old 10-25-2004, 05:43 AM
kski kski is offline
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Water Freezes the Same Temp Everywhere

Only the boiling point of water is affected by a degree or two. But the freezing point remains the same 0 degrees Celcius.
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Old 10-25-2004, 08:10 AM
Desmostylus Desmostylus is offline
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Quote:
Originally Posted by kski
Only the boiling point of water is affected by a degree or two.
A lot more than a degree or two. At the top of Everest, the boiling point is 31 K lower than at sea level.

http://en.wikipedia.org/wiki/Boiling_point
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  #17  
Old 10-25-2004, 08:16 AM
Polycarp Polycarp is offline
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Quote:
Originally Posted by Chronos
It may be possible there; I can't speak to that. But it's not the only place. There's almost certainly liquid water beneath the ice on Jupiter's moon Europa, and I wouldn't be surprised to find it in/on any of the other gas giant moons, either. It might even be possible to have liquid water deep inside the gas giants themselves.
True -- and I knew that as I was writing. Somewhere in my statement there was a phrase about "on the planetary surface" that got deleted as I revised my draft post.
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  #18  
Old 10-25-2004, 09:14 AM
David Simmons David Simmons is offline
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Quote:
Originally Posted by Polycarp
True -- and I knew that as I was writing. Somewhere in my statement there was a phrase about "on the planetary surface" that got deleted as I revised my draft post.
There's no escape. If you don't preview there are mistakes. If you do preview you leave something out. God is frowning at us all - with both eyebrows.
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