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Does the kinetic theory work for solids?

  1. Nov 20, 2015 #1
    Hello all,

    i have been asked a question about a lump of iron being warmed, and to calculate the difference between enthalpy and internal energy. I did some algebra and found that the change in the product pV , in the case of a liquid would suffice. But, since the volume doesn't change (Assumed, still solid) the change is down to the pressure. Now, for a gas, pV/T is a constant so i would argue that if T increases, p should increase. But does this whole idea work for a solid? does it exert a pressure, and does it manifest in such a form that my fluid derivations (pV/T = constant) hold for said solid?


  2. jcsd
  3. Nov 20, 2015 #2
    Don't think so. A lot of things that hold true for gases such as weak attractive forces, large intermolecular distances etc. just aren't true for solids. So the same laws don't apply.
  4. Nov 21, 2015 #3


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    Just look at the assumptions that are the basis of simple Kinetic Theory. The gas laws, based on simple kinetic theory, fail as soon as the molecules start to interact (as the gas is more and more compressed). Once that happens, some of the internal energy takes the form of Potential Energy (bonds stretching and compressing; referred to as Van der Waall's forces etc.). In a solid or liquid, this is a massive factor as the molecules are all so close together.
  5. Nov 21, 2015 #4


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    As has been eluded to, you should have learned about the assumptions of the kinetic theory of gases. So look at them and figure out how many of those assumptions are not valid for a solid. Have you done this?

    If you have, and it still doesn't answer your question, then please explain why you think all of the assumptions are still valid for a solid.

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