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Thermal Equilibrium between a Hot and Cold Body

  1. Aug 9, 2012 #1
    Just a quick question relating to thermal equilibrium between a hot and cold body. If a hot body and cold (closed systems) are opened up to each other, the thermal energy will be transfer from the hot body to cold body through conduction. So even when thermal equilibrium is reached, the temperature may be constant (closed system) but the molecules within combined bodies do not all contain the same kinetic energy right? So they will continue to collide and gain and lose kinetic energy for infinity basically right even though the overall temperature remains constant? Sorry im just trying to make sure I'm not making incorrect conclusions.

    Any help would be greatly appreciated, thanks :)
  2. jcsd
  3. Aug 9, 2012 #2
    Yes I think I understand what you are asking.

    The average kinetic energy of the molecules is closely related to temperature so will never be zero except at absolute zero. As with all averages it is a bulk composite of a range of values.

    Incidentally if you allow heat transfer by direct contact, as you describe, the process is thermodynamically irreversible.
  4. Aug 10, 2012 #3


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    Science Advisor

    You will end up with a Boltzmann distribution of energies in each accessible degree of freedom. For gas molecules, this will give a Maxwell-Boltzmann distribution of translational kinetic energies.
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