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Grade: Upto college level


how can we calculate constants 'a' & 'b' of vanderwall gas equation? plz if by graph then provide us with the detailed procedure. thanks best regards Muhib Ullah Afridi

9 years ago

Answers : (1)

879 Points

Dear student,

  • The vanderwall equation is given by

  • Here a and b are constants particular to a given gas.
  • The parameter a is related to intermolecular attractive force between the molecules , and n/V is the density of molecules
·     The term containing "a" is added to the pressure P. In other words the corrected pressure is slightly larger than the observed pressure.
·    As the  molecule moves toward the wall all of its gaseous neighbors are behind it, thus any intermolecular forces acting on the molecule are slowing it as it moves toward the wall.
·         The molecule striking the wall does so at a velocity that is slightly less (determined by the size of the intermolecular forces) than it would without these forces.
·         Or, the observed prssure is actually slightly less than the pressure would be without the intermolecular forces.
·         To correct for this, a small positive pressure must be added to the observed pressure, hence the term with "a" in it is positive.

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Askiitians Expert

Sagar Singh

B.Tech, IIT Delhi

9 years ago
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