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Heat Exchange Help Please!

  1. Nov 21, 2012 #1
    I need help with a question. I think I have an answer, but don't know if it's right. It also doesn't add up to 0 if I plug in the final temperture into the equation. But I keep getting the same answer. Help please!

    A 150 g piece of copper at 90°C is placed in 250 g of water at 20°C. Assume that no heat escapes into the surroundings. Find the final temperature of the mixture.

    mass of copper: (0.150kg)
    specific heat capacity: (390J/(kg°C))
    temperture of copper: (t2-90°C)

    mass of water: (0.250kg)
    specific heat capacity: (4200J/(kg°C))
    temperture of water: (t2-20°C))

    equation: (mass of copper)(spec. heat cap.)(final temp - intial temp) + (mass of water)(spec. heat cap.)(final temp - initial temp) = 0

    (0.150kg)(390J/(kg°C))(t2-90°C)+(0.250kg)(4200J/(kg°C))(t2-20°C))=0
    1108.5t2=26265
    t2 = 23.7°C
     
  2. jcsd
  3. Nov 21, 2012 #2
    Heat Exchange of Copper and Water

    1. The problem statement, all variables and given/known data

    I need help with a question. I think I have an answer, but don't know if it's right. It also doesn't add up to 0 if I plug in the final temperture into the equation. But I keep getting the same answer. Help please!

    A 150 g piece of copper at 90°C is placed in 250 g of water at 20°C. Assume that no heat escapes into the surroundings. Find the final temperature of the mixture.

    mass of copper: (0.150kg)
    specific heat capacity: (390J/(kg°C))
    temperture of copper: (t2-90°C)

    mass of water: (0.250kg)
    specific heat capacity: (4200J/(kg°C))
    temperture of water: (t2-20°C))

    2. Relevant equations


    equation: (mass of copper)(spec. heat cap.)(final temp - intial temp) + (mass of water)(spec. heat cap.)(final temp - initial temp) = 0

    3. The attempt at a solution

    (0.150kg)(390J/(kg°C))(t2-90°C)+(0.250kg)(4200J/(kg°C))(t2-20°C))=0
    1108.5t2=26265
    t2 = 23.7°C
     
  4. Nov 21, 2012 #3

    ehild

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    Re: Heat Exchange of Copper and Water

    Correct solution!


    ehild
     
  5. Nov 21, 2012 #4

    haruspex

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    2016 Award

    It's just rounding error. If you plug in 23.6942 you'll get something close to 0. But don't change your answer to that. 23.7 C is fine.
     
  6. Nov 21, 2012 #5
    Thanks! I appreciate it and the speedy reply!
     
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