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Understanding of irreversibility

  1. Jan 12, 2007 #1
    The thermodynamic explanation of irreversibility - does it include the microscopic view of a process, i.e. the expansion of a ideal gas (the random movement of the molecules) or the melting of an ice cube?
    Or is it only defined within the macroscopic world?
  2. jcsd
  3. Jan 12, 2007 #2
    It's defined in both:


    # 2.1 Macroscopic viewpoint (classical thermodynamics)
    # 2.2 Microscopic viewpoint (statistical mechanics)
  4. Jan 12, 2007 #3

    Andrew Mason

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    Irreversibility, of course, is the opposite of reversibility. A reversible process is one that can change direction with an infinitessimal change in conditions. In reality, all processes are somewhat irreversible. An example would be the expansion of a gas caused by applying a pressure to a container wall that was infinitessimally lower than the pressure of the gas. An infinitessimal increase in pressure will reverse the expansion and result in a compression of the gas.

    In thermodynamics, reversibility is definitely a macroscopic concept. It has no meaning at the molecular level. Pressure and temperature are macroscopic concepts that relate to qualities of large numbers of molecules and are not defined at the molecular level.

  5. Jan 13, 2007 #4
    Ok, thanks. Just had to be sure.
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