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Homework Help: Find the difference in entropy between a cup of water and a cup of ice

  1. Feb 11, 2009 #1
    Find the difference in entropy between a cup of water and a cup of ice for each of these cases:
    1. both are at T=0C
    2. ice is at T=0C water is at 20C

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    If the "water" is at 0C then it is ice right? and the difference in entropy is 0 correct?

    For the second part... do you think I am supposed to find the Q for each one? since the equation for Q is Q=cmT I don't think this would make sense because the equation for entropy (S) is S=Q/T. For ice it would be 0/0 and you can't do that....

    Do you think maybe he's asking for the change in entropy if you mix the two together?

    Thanks.

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    EDIT

    I just remembered the equation is Q=cmdeltaT

    So this must mean that he does want to know the change of entropy in the system if you mix the two together??
     
    Last edited: Feb 11, 2009
  2. jcsd
  3. Feb 11, 2009 #2
    First I'll address the conceptual problem:
    Ice is not simply water at T=0C, there is change in energy associated with melting/freezing. I think this might give you a bit of a start on the first part.

    The next issue to address:
    We have [tex] Q = S T[/tex]
    The first question that crosses my mind is what are the units on T?
    Should it be K? C? F? R? I think the answer to this question will relieve your divide by zero error.
     
    Last edited: Feb 11, 2009
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