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General Science => General Science => Topic started by: kdlynn on 26/05/2007 02:36:58

Title: boiling temperature for water
Post by: kdlynn on 26/05/2007 02:36:58

according to my family in colorado, the water boils faster in higher altitudes but it is not as hot as it should be. why would altitude cause this?

Title: boiling temperature for water
Post by: another_someone on 26/05/2007 03:57:15

Simple answer - air pressure.

The opposite happens when to boil water in a pressure cooker, as when you heat water in a pressure cooker, as the temperature builds up, so the pressure builds up in the cooker, so it delays the boiling of water until you get to a higher temperature.

Because water expands as steam (there are other factors as well, but that is the simplest to visualise), so the more pressure you apply to is, the more difficult it is to convert to steam.  If you place water in a vacuum, it will evaporate immediately (it will go straight from ice to steam, and will not stay in liquid form).

So, as you move up in altitude, air pressure becomes less, and water boils at a noticeably lower temperature.

Title: boiling temperature for water
Post by: kdlynn on 26/05/2007 04:04:28

wow. thanks

Title: boiling temperature for water
Post by: kdlynn on 26/05/2007 04:10:48

wait. hold on. so let's say that we somehow started a fire in the ocean. how hot do you think it would have to be to boil water at the bottom of the ocean?

Title: boiling temperature for water
Post by: kdlynn on 26/05/2007 04:11:42

or more probably, very far down under ground

Title: boiling temperature for water
Post by: another_someone on 26/05/2007 04:52:26

Underground is easy - just add the extra air pressure, and increase the boiling point accordingly.

The bottom of the ocean is going to get very complicated.  Firstly, you are dealing with salt water, and secondly, you might get local boiling, but it would not reach the surface unless you could warm up the water column above you.  There are submarine volcanoes that are several hundred degrees Celsius that never get to boil the oceans.  There are even organisms that are living in water well over 100 Celsius (near these submarine volcanoes), but because the water is not boiling, they can adapt to the heat.

Title: boiling temperature for water
Post by: kdlynn on 26/05/2007 04:57:59

does any of this effect the water freezing?

Title: boiling temperature for water
Post by: another_someone on 26/05/2007 05:32:30

Quote from: kdlynn on 26/05/2007 04:57:59

does any of this effect the water freezing?

Yes, but the relationship is quite complex in that regard.

We had a thread on this a little while back - will have to look it up.

Most substances will shrink when they freeze, so compressing the substance will raise its freezing point.  Water is peculiar in that it expands when it freezes, so you go through different states as you compress it around its freezing point.

http://www.thenakedscientists.com/forum/index.php?topic=7243.msg75519#msg75519