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Thermodynamics - Internal energy of state

  1. Aug 26, 2013 #1
    I had a question :

    Heat energy was supplied to melt ice at -15 degree Celsius. But it was not enough to turn the ice completely into water at 0 degrees.

    From my calculation I obtained that a mixture of 60% water and 40% ice was produced as a result of heating.

    Finally it said to describe the internal energy of that mixture. I couldn't managed to do that part. So I was wandering what was the answer to it.

    Also what determines its internal energy ?
     
    Last edited: Aug 26, 2013
  2. jcsd
  3. Aug 26, 2013 #2

    Pythagorean

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    homework-like questions should be asked in the homework section :)

    Energy does work in two different way on substances. Consider a fixed pressure environment where you add energy by heating only. First it heats them up... but then if they reach a transition point, they will stop increasing their temperature and they will use the energy to change phase (if it's sufficient energy for a phase transition) while staying at the same temperature.

    You should be able to use that information to answer the question.
     
  4. Aug 26, 2013 #3

    Andrew Mason

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    Apply the first law of thermodynamics Q = ΔU + W. Does the process result in any work being done? (assume that there is no change in volume). So how does the change in internal energy, ΔU, relate to the total heat flow, Q?

    AM
     
  5. Aug 26, 2013 #4
    Thanks to both of you. :)

    Keeping volume and pressure constant, Q = ΔU.

    But what's there to describe about the internal energy ?
     
  6. Aug 26, 2013 #5

    Andrew Mason

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    I think the question asks you to describe and quantify the change in internal energy. For the ice the increase in internal energy is in the form of an increase in molecular kinetic energy only. For the liquid water, there has been an increase in molecular kinetic energy and in potential energy (bonds broken).

    AM
     
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