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Homework Help: Final temperature problem

  1. Sep 27, 2009 #1
    1. The problem statement, all variables and given/known data

    if 100.0g of water at 100.0 C is mixed with 200g of water at 20.0 in an insulated container, what will the final temperature be?

    2. Relevant equations

    3. The attempt at a solution
    Since the energy change would be equal but opposite I though oh well I can leave the Q out and have (100.0)4.18(Tf-100.0)=(200)4.18(Tf-20.0). So I sorta did worked through this but started getting crazy stupid answer that I threw away. Pretty much simplified,distributed,addition and subtraction property of equality an then division property of equality
  2. jcsd
  3. Sep 27, 2009 #2


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    is correct except for trouble with signs: the left side is negative and the right side is positive. Replace the Tf - 100 with 100 - Tf.
  4. Sep 27, 2009 #3

    Thanks.. and then

    41800-418Tf=836Tf-16700(in sig figs)
    46.7C(sig fig)

  5. Sep 27, 2009 #4


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    Looks good!
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