MadSci Network: Physics

Re: Is the reduced eqn of state independent of the nature of the real gas taken

Date: Tue May 9 09:21:12 2000
Posted By: Michael Weibel, Battelle Chemist
Area of science: Physics
ID: 956677932.Ph

The Van der Waals equation  (P+an^2/V^2)(V-nb) = nRT
looks a bit like the ideal gas law, except for two correction terms.

The first term (an^2/V^2) arises from the real intermolecular attraction 
that two of the same molecules have for one another (remember in the ideal 
gas law, the two assumptions made are that gases have no volume and are 
non-interacting).  It is an additive term because interactions tend to 
lower the pressure (rearranging, P=nRT/(V-nb) - an^2/V^2).  The "a" 
constant is specific to a particular gas, and reflects its strength of 
intermolecular interaction.

The second term (nb) arises from the real volume that molecules have.  The 
true volume of the system is larger than expected, so it is a negative 
term (that is, you have to subtract the true volume of the molecules from 
the system to account for them).  as a result, the "b" constant relates to 
molecular "size"

Then, the answer to your question is "yes".  When the "a" and "b" terms 
are removed (assumed to be zero), you end up with the Ideal Gas Law, which 
is a generalization for all gases (non-specific).

Please feel free to email with further questions at

best regards,

Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2000. All rights reserved.