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Heat and temperature question with calorimetry

  1. Apr 3, 2015 #1
    1. The problem statement, all variables and given/known data
    2.0kg of a metal (for which c = 620 J kg K ) is immersed in 1.5kg of water, initially at 20◦ . What is the final temperature if 8.0 × 104J are added as heat?
    2. Relevant equations
    Q=mcΔT

    3. The attempt at a solution
    So I was able to get the correct answer what I did was:
    Qadded heat+mcΔTiron+mcΔTwater=0
    -8×104 +2(620)(Tf-293)+1.5(4200)(Tf-293)=0
    doing the algebra will give you 303.6 K which is correct...but I was just wondering why is the heat added negative?
     
  2. jcsd
  3. Apr 3, 2015 #2

    rude man

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    Homework Helper
    Gold Member

    I assume the metal initial temp. was 20C also.
    Your equation is conceptually somewhat unwieldy. More obviously,
    heat gained by water + heat gained by metal = external heat added
    which is your equation also if you move the external heat to the rhs of your equation.
     
    Last edited: Apr 4, 2015
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