Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: Liskow on 13/03/2009 17:26:10

Title: Can I lower temperature by reducing volume?
Post by: Liskow on 13/03/2009 17:26:10

Hot things tend to be a little larger than cold things.  So can I lower a things temperature by squishing it into a smaller volume?

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Title: Re: Can I lower temperature by reducing volume?
Post by: lancenti on 13/03/2009 18:05:12

This is not necessarily true.

Unit mass of water at 4 degrees centigrade has a smaller volume than unit mass of water at 1 degree centigrade, if I remember right. Water is densest at 4 degrees I believe.

However, using the ideal gas law,

pV=nRT

or Charles Law (I believe)

V₁/T₁=V₂/T₂

We find that compression should actually lead to an increase in temperature. Hence to cool a gas, you'd probably want to rapidly expand it.

Title: Re: Can I lower temperature by reducing volume?
Post by: blakestyger on 13/03/2009 18:37:45

Quote from: lancenti on 13/03/2009 18:05:12

We find that compression should actually lead to an increase in temperature. Hence to cool a gas, you'd probably want to rapidly expand it.

Yep - the Joule-Thompson effect.

Title: Re: Can I lower temperature by reducing volume?
Post by: lightarrow on 14/03/2009 10:55:24

Quote from: Liskow on 13/03/2009 17:26:10

Hot things tend to be a little larger than cold things.  So can I lower a things temperature by squishing it into a smaller volume?

Even if your first sentence were always true (but it's not) it's wrongly stated:
when you *give heat* to things they enlarge. Infact, if you compress them, you *receive heat* from them.

Title: Re: Can I lower temperature by reducing volume?
Post by: Raghavendra on 16/03/2009 09:36:59

hmmm you are at critical

          You should read raoult's law