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Heat Capacity

  1. Sep 13, 2010 #1
    1. The problem statement, all variables and given/known data
    At 25C Cu metal (at. wt. 63.54 g/mol) has a molar heat capacity of 24.4 J/molK. The density of Cu is 8.949g/cm^3 at 0C and 8.904 g/cm^3 at 100C. Assuming that Cp is temperature independent, calculate Q, W, deltaU and deltaH when 100grams of Cu metal are heated from 0C to 100C under constant pressure 1atm.

    Ans. Q=deltaH is about equal to deltaU = 3840J, W=-.0057J

    Note: deltaH is about equal to deltaU for heating of solids and liquids at constant pressure because these materials exhibit very low volume changes on heating.

    3. The attempt at a solution

    density = m/v so v=m/density so
    V1=100g/8.949g/cm^3 = 11.17cm^3 and V2 = 100g/8.904 g/cm^3 = 11.23cm^3
    W=-P(V2-V1) = -1atm((11.23X10^-2(m^3))-(11.17X10^-2(m^3)))=-.0006J about correct?

    Q=nCn(Tf-Ti)
    n=((63.54g/mol)/(100g))=.6354mol
    Q = (.6354mol)(24.4J/molK)(373K) = 5782.9J not so correct?...
     
  2. jcsd
  3. Sep 13, 2010 #2

    Borek

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    Staff: Mentor

    If you have 100g and molar mass is 63.5g, having 0.63 moles is off. It is just like stating "I have $100, this book is $50, so I can buy only a half"...
     
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