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#1
10-22-2004, 01:03 PM
 Jinx Member Join Date: Dec 1999 Location: Lost In Space Posts: 7,776
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
#2
10-22-2004, 01:21 PM
 bashere Guest Join Date: Sep 2000 Location: Toronto or Los Angeles Posts: 805
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.
#3
10-22-2004, 01:22 PM
 friedo Guest Join Date: May 2000 Location: Brooklyn Posts: 23,402
Indeed, it does. Air pressure and water freezing.
#4
10-22-2004, 01:39 PM
 bashere Guest Join Date: Sep 2000 Location: Toronto or Los Angeles Posts: 805
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.
#5
10-22-2004, 06:40 PM
 David Simmons Charter Member Join Date: Nov 2001 Posts: 12,684
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.
#6
10-23-2004, 11:28 AM
 Crafter_Man Guest Join Date: Apr 1999 Location: Ohio Posts: 10,416
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.
#7
10-23-2004, 11:45 AM
 WhyNot Guest Join Date: Jul 2004 Location: Sweet Home Chicago Posts: 33,496
Um, so (at) what temperature does water freeze in Denver?
#8
10-23-2004, 12:49 PM
 Polycarp Member Join Date: Aug 1999 Location: A better place to be Posts: 26,718
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.)
#9
10-23-2004, 03:24 PM
 Ponder Stibbons Guest Join Date: Jun 2003 Location: Dallas Posts: 5,909
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.
#10
10-23-2004, 03:48 PM
 bashere Guest Join Date: Sep 2000 Location: Toronto or Los Angeles Posts: 805
Quote:
 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.
#11
10-23-2004, 05:26 PM
 Ignatz Member Join Date: Oct 2004 Posts: 5,474
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.
#12
10-24-2004, 06:15 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 72,630
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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#13
10-24-2004, 10:40 PM
 LSLGuy Charter Member Join Date: Sep 2003 Location: Southeast Florida USA Posts: 20,116
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.
#14
10-24-2004, 11:34 PM
 David Simmons Charter Member Join Date: Nov 2001 Posts: 12,684
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.
#15
10-25-2004, 06:43 AM
 kski Guest Join Date: Oct 2004 Location: Canada Posts: 14
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.
#16
10-25-2004, 09:10 AM
 Desmostylus BANNED Join Date: Nov 2002 Location: Sydney Posts: 5,539
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
#17
10-25-2004, 09:16 AM
 Polycarp Member Join Date: Aug 1999 Location: A better place to be Posts: 26,718
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.
#18
10-25-2004, 10:14 AM
 David Simmons Charter Member Join Date: Nov 2001 Posts: 12,684
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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