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Dumping Entropy

  1. Mar 9, 2014 #1
    "Dumping" Entropy

    Hello everyone,

    I am reading Daniel Schroeder's Thermal Physics book. One phrase he uses that I find particular confusing is that a system has to "dump" entropy. As one example, in chapter 5 he briefly discusses how a fuel cell functions, stating, "In the process of producing this electrical work, the
    fuel cell will also expel 49 kJ of waste heat, in order to get rid of the excess entropy
    that was in the gases."

    Why does something have to get rid of excess entropy, could someone help me in understanding why this is so?
     
  2. jcsd
  3. Mar 9, 2014 #2

    Andrew Mason

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    Since entropy is not conserved it is difficult to conceptualize it as something physical. It is just a mathematical quantity associated with a thermodynamic state.

    Re: "dumping entropy". This suggests that the entropy flows from the fuel cell to its surroundings. It doesn't. Energy flows from the fuel cell in the form of heat. Total entropy increases when heat flows due to a temperature difference. The entropy increase of the cold reservoir (surroundings) is not "dumped" by the fuel cell. It never was in the fuel cell. It only came into existence when the heat flow occurred from the fuel cell to the surroundings.

    AM
     
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