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Rate of effusion dependance on pressure

  1. Feb 12, 2012 #1
    In my class rate of effusion was told to be directly proportional to the mean speed of gas molecules which is intuitive and i understand. RMS speed of molecules is √3RT/M
    So rate of effusion is inversely proportional to sqaure root of molar mass

    But i dont understand how rate of effusion is directly proportional to pressure
    RT = PV
    So RMS speed = √PV/M so rate of effusion should be proportional to square root of pressure right? But apparently its not, plz explain me why

    Thank you!
  2. jcsd
  3. Feb 14, 2012 #2
    It makes more sense if you replace PV=RT with the statistical mechanical equation of state,
    P = nkT. Then the number density (number of molecules per unit volume) is directly proportional to the pressure. The more molecules per unit volume, the greater the effusion through an opening.
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