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Possible violation of the Kelvin statement (2nd law)?

  1. Dec 17, 2015 #1
    Say I have an infinite cylinder filled with monoatomic gas and on one end has a piston attached to it. I now supply heat to the cylinder. The gas expands thereby converting all of heat energy into physical work(displacement of the piston). Since the cylinder is very long it eliminates the requirement of a cyclic process and could in theory provide work for a very long time until the piston reaches the cylinder's length. Have I not just violated kelvins statement? Provided friction is zero? W=P.dV?
     
  2. jcsd
  3. Dec 17, 2015 #2

    mfb

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    Why bother heating it? You have an infinite amount of energy stored in your cylinder, you can easily extract a finite amout out of it without changing the system.
    Working with infinite things just doesn't work.
     
  4. Dec 17, 2015 #3
    What if it was very long but finite? Wouldn't then all the Q I supply be converted to work?
     
  5. Dec 17, 2015 #4

    mfb

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    If you have an infinite vacuum of zero temperature available, and infinite time for the process.
     
  6. Dec 17, 2015 #5
    How are you supplying heat though? A flame, electricity, a hamster on a wheel? That is where the increase in entropy is occurring here.
     
  7. Dec 19, 2015 #6
    I still haven't been exposed to the idea of entropy yet. Basically I mean that if the cylinder is very long for some finite amount of time I could get all of the heat energy to be expand the gas and thereby converting "all" heat into work.
     
  8. Dec 19, 2015 #7

    mfb

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    If you have a perfect vacuum (or anything else) at zero temperature as cold reservoir, you can convert heat to mechanical power with an efficiency of (nearly) 100%.
     
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