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Heat Capacity and Thermal Equilibrium

  1. Dec 2, 2014 #1
    1. The problem statement, all variables and given/known data
    A 3.50-kg block of iron initially at 8.00 × 10^2 K is placed on top of a 6.25-kg block of copper initially at 4.00 × 10^2 K. Assume the blocks are thermally insulated from their surroundings but not from each other and that they constitute a closed system.

    How much energy is transferred thermally from the iron to the copper as the two blocks come to thermal equilibrium?
    2. Relevant equations
    heat capacity=amount of energy transferred thermally (J)/resulting change in temperature
    specific heat capacity (c) =amount of energy required to raise 1 kg of a certain material by 1 degree Kelvin (J/K*kg)

    c of copper is 385, c of iron is 449


    3. The attempt at a solution
    Thermal equilibrium would be (400+800)/2=600. So during this process the copper would be raised 200 K. Using the specific heat capacity of copper 385 J/K*kg, I found that it would be 2406.25 J to raise 6.25 kgs of it by 1 K. To Raise 200 K it would be (2406.25)(200)=481250 J.

    This is incorrect, however. What am I missing?
     
  2. jcsd
  3. Dec 2, 2014 #2

    haruspex

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    No. Any other thoughts?
     
  4. Dec 2, 2014 #3
    They do not contribute to the equilibrium temperature equally do they? I looked up a formula for finding equilibrium temp and otherwise worked it out the same. I got the right answer, thanks!

    Formula for Equilibrium Temperature: c1m1(Tf-Ti)=c2m2(Tf-Ti)

    -(449)(3.5)(Tf-800)=(385)(6.25)(Tf-400) Final Temperature= 558 K, so the copper is only raised 158 degrees.
     
  5. Dec 2, 2014 #4

    haruspex

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    Good job.
     
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