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Block of ice melts - entropy of ice?

  1. Jul 26, 2008 #1
    1. The problem statement, all variables and given/known data
    A 2.00 kg block of ice at 0.0˚C melts. What is the change in entropy of the ice as a result of this process?


    2. Relevant equations
    Q = mcΔT
    ΔS = Q/T



    3. The attempt at a solution
    Q = (2.00 kg)(2.1 kJ/kg*K)(273 K)
    Q = 1092 J

    ΔS = 1092 J / 273 K
    ΔS = 4 J/K


    Any good?
     
  2. jcsd
  3. Jul 26, 2008 #2

    Mapes

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    Re: entropy

    Not good. Why would you calculate Q using an equation with ΔT? The temperature change is zero, not 273 K. I like your second equation, though, which assumes constant temperature.

    How about getting the energy from the phase change?
     
  4. Jul 26, 2008 #3
    Re: entropy

    Then I'm not sure how to do the problem, the first part anyway, because then Q = 0 and if Q = 0 then ΔS = 0 as well...
     
  5. Jul 26, 2008 #4

    Mapes

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    Re: entropy

    How about looking up the energy associated with the phase change?
     
  6. Jul 26, 2008 #5
    Re: entropy

    Ahhh... so I'm looking at latent heat then?
    Q = mass x latent heat of fusion
    Q = (2.00 kg)(333.7 kJ/kg)
    Q = 667.4 kJ


    Better? And then plug that into the second equation?
     
  7. Jul 26, 2008 #6

    Mapes

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    Re: entropy

    Better.
     
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