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Does Evaporation absorb heat?

  1. Dec 12, 2013 #1
    1. The problem statement, all variables and given/known data
    For which process does the system absorb energy in the form of work?
    a) Water Evaporates into steam.
    b)Air is compressed by a bicycle pump.
    c) Both


    2. Relevant equations



    3. The attempt at a solution

    I though the answer was both. However, the key says the correct answer was just B. Why would it not be A as well? I thought evaporation required the input of energy.
     
  2. jcsd
  3. Dec 12, 2013 #2

    mfb

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    Staff: Mentor

    Work is a specific form of energy. While (a) needs energy, it will not use work.
     
  4. Dec 12, 2013 #3
    I was thinking that maybe although the energy went into the steam they system is the water which would have cooled.
     
  5. Dec 12, 2013 #4

    mfb

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    Usually the water will cool down, indeed.
     
  6. Dec 12, 2013 #5
    So what exactly is work then?
     
  7. Dec 12, 2013 #6

    mfb

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    Work
    A force acting over some displacement. There is no such force or displacement involved in evaporation.
     
  8. Dec 12, 2013 #7

    Qube

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    Force applied over some unit of distance. If you push against a car and it moves, you've done work.

    If you push on a wall, and the wall doesn't move or fall over, then you've done no work. The displacement of the wall here is 0. Now if the wall does fall over then you've done work. Good work!

    (Or bad)
     
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