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Author Topic: What happens as liquid nitrogen becomes a gas?  (Read 7338 times)

R Uptigrove

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What happens as liquid nitrogen becomes a gas?
« on: 04/06/2008 10:50:00 »
R Uptigrove asked the Naked Scientists:

If you put, let's say a pint, of liquid nitrogen in an unbreakable quart container and let it rise to room temperature, 75F, what will the pressure be?

Will it all become a gas?  If so, then a follow-up question is how cold does the environment have to be where some of the nitrogen remains a liquid?

At that temperature I would assume that the amount of original liquid would not affect the final pressure as long as some liquid was left.

Thanks, whoever you are, wherever you may be.

Bob, old enough where four score and seven years doesn't sound so awfully long as it did when I was your age.

What do you think?


 

Offline RD

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What happens as liquid nitrogen becomes a gas?
« Reply #1 on: 04/06/2008 18:46:27 »
If you put, let's say a pint, of liquid nitrogen in an unbreakable quart container and let it rise to room temperature, 75F, what will the pressure be?

The tanks used to contain liquid nitrogen can withstand pressures of 350 psi ...
http://www.apsusa.biz/grams/safetygram7.pdf
[hopefully this includes a large margin of safety]
 

Online Bored chemist

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What happens as liquid nitrogen becomes a gas?
« Reply #2 on: 04/06/2008 19:08:28 »
Don't try the experiment unless you are really sure that the container is unbreakable- otherwise it makes quite a good bomb.
Anyway, the answer is that the nitrogen, as it warmed, would beccome a supercritical fluid.
http://en.wikipedia.org/wiki/Supercritical_fluid
Effectively that's too dense to be a gas, but too hot to be a liquid- so it's neither.

If the ambient temperature were about 200 degrees below freezing (that's below 77K to those who like SI units) the nitrogen wouldn't boil at all. Provided that the temperature is below the critical temperature for nitrogen (-146.9C) you can get a liquid if the pressure is high enough. If the temperature is above that then, no matter how high the pressure, you can't get a liquid.
Interestingly, the critical pressure of nitrogen is quite low (about 33.5 atmospheres) so the "gas" in cylinders of nitrogen, as sold for welding and such, is a supercritical fluid already.
 

Offline Madidus_Scientia

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What happens as liquid nitrogen becomes a gas?
« Reply #3 on: 05/06/2008 10:36:29 »
What's the go when science teachers get a little tub of it and dip things into it and then shatter it, why doesn't it explode into gas as soon as they open it up?
 

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What happens as liquid nitrogen becomes a gas?
« Reply #4 on: 05/06/2008 21:32:53 »
Because it's very cold.
 

Offline Madidus_Scientia

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What happens as liquid nitrogen becomes a gas?
« Reply #5 on: 07/06/2008 01:04:28 »
So while its under pressure in the cylinder it can't absorb heat? and only begins absorbing it again when you release the pressure on it?
 

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What happens as liquid nitrogen becomes a gas?
« Reply #6 on: 07/06/2008 18:06:56 »
The nitrogen in cylindes is technically a supercritical fluid- but it acts pretty much like a gas under high pressure. Whan you open the valve the gas comes out.
Liquid nitrogen is stored at near atmospheric pressure and very low temperature in Dewar vessels.
 

Offline Madidus_Scientia

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What happens as liquid nitrogen becomes a gas?
« Reply #7 on: 08/06/2008 02:35:13 »
I see. How do they cool it so much in the first place, really hardcore freezers?
 

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Offline qazibasit

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What happens as liquid nitrogen becomes a gas?
« Reply #9 on: 13/06/2008 12:42:16 »
while converting from liquid to gas it will make the surrounding cooler and if there is a large volume of liquid nitrogen it may even cause the freezing of its surrounding.
 

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What happens as liquid nitrogen becomes a gas?
« Reply #9 on: 13/06/2008 12:42:16 »

 

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