# Nonlinear gas volume/pressure relationship

is there a gas which its volume increases nonlinearly with decrease in pressure?

## Answers and Replies

A non-linear relation is in fact the most common in practical cases ('real gases', they are called).
A modified equation of the ideal gas equation exists which explains this (it's called the 'Van der Walls gas equation):

(P + an^2/V)(V - nb) = nRT

Here, a and b are constants. 'a' accounts for inter-molecular forces, and 'b' accounts for the volume of the gas atoms themselves.

A non-linear relation would imply that the inter-molecular forces increase rapidly with compression, and, this is possible if the gas particles are charged....is that the kind of thing you have on your mind??

thanks a lot!
is there a table of gas names and their volume pressure values?

I don't know about a table (you could probably find one if you searched on the net enough anyways), but you will be ale to find plenty of graphs plotting P versus V for various gases at different temperatures.
But these probably wouldn't help you too much - because they are inversely proportional, you should be getting a rectangular hyperbola in an ideal case, and the little deviations that would occur for a real gas would not be noticeable, especially because of the peculiar shape of the graph...
A better graph would be one which plots compressibility (represented by the variable 'Z') versus pressure. Now this is a graph from which you can learn a lot, and you can clearly see major deviations of real gases from an ideal case. There's a lot you can learn from this, and it's really extensive, so I suggest you search for it on the net. In fact, if you could log on to ncert.nic.in
That's the website from which you can access all the textbooks used in India for all grades. In Grade 11's Chemistry (Part I) textbook, read the sections on 'Real Gases' in the fifth chapter (titled 'States of Matter')...that should help you a lot - they've written about the stuff really well...

Hope this helps!