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Homework Help: Thermodynamics problem#1

  1. Jun 9, 2007 #1
    1. The problem statement, all variables and given/known data

    When there is a heat flow out of the system during a reversible isothermal processthe entropy of the system decreases.Why does this not violate the 2nd law of thermodynamics?

    2. Relevant equations
    3. The attempt at a solution I hope this is correct.Please check and confirm.

    Because the question uses the word "system" quite loosely. They are using "system" to mean the gas or other working substance from which the heat flows. But in terms of the second law, the word "system" refers to everything that loses or gains heat during the process.

    So while the gas releases heat and the entropy of the gas decreases, the heat is absorbed by the environment (which must be included in the "system") and the entropy of the environment increases. Overall the total change in entropy is positive, as the increase for the environment is greater than the decrease for the gas.
  2. jcsd
  3. Jun 9, 2007 #2
    when there is a decrease in this enrophy, the entrophy of the surroundings increases, u are quite right. system in the law refers to everything
  4. Jun 9, 2007 #3
    OK thank you.
  5. Jun 10, 2007 #4
    In fact, if it's reversable, then the entropy increase of the surroundings exactly matches the entropy decrease of the system.
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