Most real gases at standard temperature and pressure do not deviate too far from pV=nRT . Even when they do, the ideal gas equation still provides a good model for qualitative understanding of how the state varibles p, V and T play out.
Check out the following demonstrations!
See xmdemo.wordpress.com/089 for detail
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See xmdemo.wordpress.com/012 for detail
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See xmdemo.wordpress.com/060 for detail
xmPhysics 