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Change in Entropy

  1. Mar 18, 2010 #1
    1. The problem statement, all variables and given/known data

    An 8.5 g ice cube at -10°C is put into a
    Thermos flask containing 200 cm3
    of water at 20°C. By how much has the
    entropy of the cube-water system changed when equilibrium
    is reached? The specific heat of ice is 2220 J/kg·K.

    Cw= 4190
    Mi= 8.5
    Mw= 200
    Lf= 333000
    Ci=2220



    2. Relevant equations

    Tf=cw*mw(20)-mi(lf+10ci)/mw*cw+mi*cw

    Tf= 288.73 K


    mi*ci*ln(273.15/263.15)+lf*mi/273.15+mi*cw*ln(288.73/273.15)+mw*cw*ln(288.73/293.15)







    3. The attempt at a solution

    .70366+10.36+1.975-6.365

    I got 6.67 J/k. But I'm not sure thats right.
     
  2. jcsd
  3. Mar 18, 2010 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    It is not very clear what you are trying to do here.


    The first thing you have to do is figure out whether all the ice melts. If it does, you then have to figure out what the final temperature is.

    Then you have to work out what the change in entropy of the ice is in reaching 0C, in changing to water, and in rising to the final temperature. Use the definition of incremental change in entropy: dS = dQ/T.

    Then you have to work out the change in entropy of the 200 g of water in cooling to the final temperature.

    AM
     
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