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Homework Help: Another problem dealing with heat transfer

  1. Sep 27, 2009 #1
    1. The problem statement, all variables and given/known data
    How much Fe at 200.0C must be placed in 100.00g of water at 20C so that the temperature of both will be at 35.0?

    2. Relevant equations

    3. The attempt at a solution
    Energy required to raise water is 6300 J
    So I did by:
    (keep in mind I used sig figs)

    And then..

    I assumed I must plug in 6300 as a negative to the FE to get the amount needed
    I did

    I go to check my work by doing taking out the final temp and trying to solve for it by using the grams

    I did so by:
    And got 48.7 Which is not so close to 35C

    Am I checking this wrong or am I doing the problem wrong?
  2. jcsd
  3. Sep 27, 2009 #2


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    Homework Helper

    I think you have done the problem correctly and the problem with the check is that the "35-Tf" should be "Tf - 20".

    You know, your work would be so much clearer if you put in a few words like this:
    Heat lost by iron = heat gained by water
    mC(delta T) = mC(delta T)
    m(.449)(165) = 100*4.18*15
    m = 100*4.18*15/(.449*165) = 84.6 g
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