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Specific heat capacity and final temperature

  1. Sep 23, 2012 #1
    1. The problem statement, all variables and given/known data

    A 2.8 kg sample of a metal with a specific heat of 0.43KJ/KgC is heated to 100.0C then placed in a 50.0 g sample of water at 30.0C.* What is the final temperature of the metal and the water?


    2. Relevant equations

    heat loss by the metal = heat gain by the water

    3. The attempt at a solution

    I solve it this way:
    2800 g x 430 J/gC x (Tf-100) = 50 g x 4.2 J/gC x (Tf - 30)

    my final answer is 100 C,

    please help me check what makes my answer wrong because the answer on the key is 97C...

    Thanks a lot....
     
  2. jcsd
  3. Sep 23, 2012 #2
    i solve it again and i got 114 as the answer because of 0.43KJ/KgC, it will be 0.43J/gC... Please help me with this one, what makes it wrong?
     
  4. Sep 23, 2012 #3

    ehild

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    Check the red one. Is it really the heat lost by the metal?


    ehild
     
  5. Sep 23, 2012 #4
    is it 2800 g x 0.43J/gC x 70 C?
     
  6. Sep 23, 2012 #5

    ehild

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    You said that the heat lost by the metal is equal to the heat gained by water.
    The metal cools down from 100 C° to Tf, how much heat releases in the cooling process?

    ehild
     
  7. Sep 23, 2012 #6
    i think it should be100C - tf, since there is a decrease in temperature. my answer is 90C, is that correct?
     
  8. Sep 23, 2012 #7

    ehild

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    Yes, you need to calculate with 100-Tf, but I got different result. Do not drop significant digits during the calculations.

    ehild
     
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