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Homework Help: Van der waals equation

  1. Apr 17, 2012 #1
    1. The problem statement, all variables and given/known data

    (P+ an^2/V^2)(V-nb) = nRT
    I'm having some problems in understanding the above equation.

    firstly, PV=nRT holds for ideal P and V , so after correction we are writing ideal P and V in terms of measured P and V right?

    secondly V-nb is the actual volume not the ideal one. isnt it? if yes what is it doing in the above equation?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Apr 18, 2012 #2
    please reply.....i'm going mad:mad::mad:
  4. Apr 18, 2012 #3


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    No. This is an approximation that is somewhat better than the simple form of the IGE.
    V-nb is a correction to the volume that is proportional to the number of moles of gas and has units of volume. Recall that the IGE assumes that gas molecules/atoms are non-interacting and have no "size".
  5. Apr 18, 2012 #4
    okkk....i was unable to understand the corrections made by van der waals in IGE....would u pls check if i'm getting it right...

    in PV=nRT V is the volume that is available to the gas molecules, since at ideal gas conditions(high T and low P) the volume of particles is negligible,we can write the volume as V only....but in other cases we write V-nb taking into account the volume of particles too.
    and in PV=nRT P stands for the pressure that gas particles would exert if no inter molecular forces were present....so in ideal conditions this is approximately equal to measured P.....in other cases we have to add an^2/V^2
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