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Conditions when real gases behave as ideal gases

  1. May 15, 2012 #1
    Well i know real gases behave as ideal gas (almost) when pressure is low and temperature is high. I want to understand this - When pressure is low attractive forces in the gas moelcules will be stronger(as compared to high pressure) but the fast movement due to high temperature compensates it? Am i right?

    Why can't it be high pressure and low temperature? Because of high pressure repulsive forces dominate ( because molecules will be very close) but then you lower the temperature and moelcules don't move very fast and that compensates for the repulsive forces

    Anything wrong in my reasoning. Please help!
  2. jcsd
  3. May 15, 2012 #2


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    Staff: Mentor

    Do you remember assumptions used in the kinetic theory?
  4. May 15, 2012 #3
    Yes - molecules have negligible size
    no intermolecular forces
    elastic collisions
  5. May 15, 2012 #4


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    Staff: Mentor

    No intermolecular forces or negligible intermolecular forces (apart from collisions).

    Start from there. What can you say about intermolecular distances in the gas that has a low pressure and a high temp?
  6. May 15, 2012 #5
    well in case of low pressure and high temperature - there will be large intermolecular distances so negligible intermolecular forces. So it well behave as an ideal gas. I understand now - thank you

    And if there is high pressure there will be repulsive forces and small distances which does not match with the postulates. Thank you again

    But one more question - not closely related to my previous question
    In the real gas equation pressure is P + an2/V2. Is the correction term only for attractive forces , only for repulsive forces or both? If its for both does that mean value of "a" changes according to conditions
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