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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: shehri on April 15, 2007, 01:27:47 AM

Title: Heating on compression
Post by: shehri on April 15, 2007, 01:27:47 AM

I know that expansion of gases causes adiabatic cooling due to Joule-thomson effect.But why gases produce heating on compression, I want to know.
Plz. throw some light on both i.e causes of cooling on adiabatic expansion & compression.Thanks.

Title: Re: Heating on compression
Post by: allanf on April 15, 2007, 02:04:27 AM

Not all gases cool when expanded, it depends on the gas in question and the temperature over which the process occurs.  Many gases have inversion temperatures, when warmer than a certain temperature the Joule-Thompson coefficient is negative and expansion causes them to warm, below this temperature and expansion causes them to cool.  For air I think the inversion temperature is ~325C.  Heating (or cooling) upon compression comes from the same effect, just in reverse.

The Joule-Thompson effect itself is a consequence of the internal energy of non-ideal gases.  Ideal gases have a Joule-Thompson coefficient of zero and do not experience heating and cooling during isocaloric compression.