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Thermodynamics Questions dealing with Entropy

  1. Mar 15, 2009 #1
    My teacher gave us a packet of questions, I am stuck on a few:
    Part 1)
    1. The problem statement, all variables and given/known data
    A hot brick is tossed into cold water, and this is an adiabatic enclosure. The volume of the brick and water will not change.

    Define the system and surroundings.

    2. Relevant equations Entropy Tot = Entropy of system + Entropy of surroundings
    3. The attempt at a solution
    I am assuming the water is the surroundings, and the brick the system, or is it supposed to be a tricky question?

    Part 2)
    1. The problem statement, all variables and given/known dataWhat will happen in terms of temperature changes, after the brick is tossed into the water? Is this answer based on the First Law of Thermodynamics? Explain why or why not.

    2. Relevant equations First Law of Thermodynamics: dU=dQ-dW
    3. The attempt at a solutionI am pretty sure that the brick's temperature will go down, and the water's temperature will go up, but it sais that the process is adiabatic so no Heat is given of. I am not sure how to relate these two, maybe there will be no Temp. change?

    Part 3)
    1. The problem statement, all variables and given/known dataWhat will be Utotal for the process described in part 2? Explain your reasoning.Is the answer based on an application of the 1st Law of thermodynamics? Explain why or why not.

    2. Relevant equations First Law of Thermodynamics: dU=dQ-dW
    3. The attempt at a solution U=W, because the process is adiabatic, not Q is given of. How do I relate it to 1st Law of Thermo then?



    Thank you so much for any help!
     
    Last edited: Mar 15, 2009
  2. jcsd
  3. Mar 15, 2009 #2

    Q_Goest

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    Hi ana. Welcome to the board. :smile:

    When they say "adiabatic" they don't mean there is no heat transfer between the water and brick, they mean there is no heat transfer between the water + brick and the surroundings. In other words, consider the water and brick being inside a perfectly insulated bath tub.

    Does that help at all?
     
  4. Mar 17, 2009 #3
    It does help indeed!
    Thank you for the clarification! :smile:
     
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