From the Amagat's curve we can see two types of result for real gases.

  1. If we increase pressure,the value of $PV$ decreases initially and then the value starts increasing for the gases like- carbon dioxide, nitrogen, oxygen, methane, etc..
  2. If we increase pressure,the value of $PV$ starts increasing initially for the gases like - hydrogen, helium, etc.

Now please explain what're the reasons behind this kinda behaviour of real gases?

  • $\begingroup$ This seems like a homework question. We ‎have a policy which states that you should show your thoughts and/or efforts into solving the ‎problem. It'll make us certain that we aren't doing your homework for you. Otherwise, this ‎question may get closed. $\endgroup$
    – bon
    Jun 30, 2015 at 17:53
  • $\begingroup$ @Bon this isn't necessarily homework. I see it more as erratum. It does deal with something in the textbook, just that it doesn't look for an error. $\endgroup$
    – M.A.R.
    Jun 30, 2015 at 17:56
  • $\begingroup$ I think it's just bad tag 'cause it doesn't look like erratum. $\endgroup$
    – Mithoron
    Jun 30, 2015 at 18:15
  • $\begingroup$ @Mithoron I scratched my head for the tags. I, am the guilty fugitive who added erratum. Can you please add better tags? $\endgroup$
    – M.A.R.
    Jun 30, 2015 at 19:37

1 Answer 1


The ideal gas law can be derived using kinetic molecular theory by making two very important assumptions that are not true for real gases:

  1. There is no attractive force between gas molecules
  2. The gas molecules have no volume

Think about how the PV curve would change when you remove one or both of these conditions. Then think about which types of molecules the assumption of "no attractive force" would be more important for.


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