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Can the gas law be applied at high temp?

  1. Feb 22, 2007 #1
    Recently on forum we have several topics about the ideal gas law which involve the high and low pressure. Now I wonder if this law can be applied at rather high temperatures, let say 1000-1200 K, but the pressure is just ambient.

    Thank you for reading the question.
    THL
     
  2. jcsd
  3. Feb 22, 2007 #2
    I would say that higher the temperature the better the perfect gas law should work.

    This is because the short range forces that cause the deviation from the perfect gas law play less and less role when the temperature (the energies) is higher. Don't forget the perfect gas law occurs when the interactions between molecules is negligible (although large enough to allow the thermodynamic equilibrium to be reached, ... , long discussion).

    However, at higher and higer temperature molecules can break down and even atom can become ionised. This cause the number of "moles" to increase and changes the volume or the pressure, and thereby cause a deviation from the perfect law in the course.

    Moreover, new forces occur since ionization will produces ions and ions will experience very strong and -in principle- long range attraction. However, in fully ionized plasma, the perfect gas law is very well verified. The reason is that this long range eletrostatic forces are shielded by cloud of electron around the ions, this is called Debye shielding. Plasma physics is a quite interresting subject ...

    Michel
     
  4. Feb 22, 2007 #3
    Thank you lalbatros.

    Your explanation is quite clear. I just think that at relatively high temperature, gas molecules may get 'softer' or something else, and that could affect the linearity of the gas law. Anyway, every law has its own domain doesn't it.
     
  5. Feb 23, 2007 #4
    Haiha,

    Clearly, when the interactions (potential energy) between molecule become negligible compared to the total energy of the molecules, then the perfect gas law become more and more precisely verified.

    As I explained, generally increased temperatures imply higer energies and constant of lower potential energies.

    However, sometimes new physics pop-up, like ionisation, and new interactions appear, like long range electrostatic forces. Then the increased validity of the perfect gas law is not granted anymore. However, Debye shielding makes comes to rescue and in hot ionised gases, the perfect gas law tend to be valid. Note also that plasmas display quite a lot of interresting physics.

    Michel
     
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