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Find the relative mass of the blocks (thermochemistry)

  1. Mar 6, 2014 #1
    1. The problem statement, all variables and given/known data
    A block of copper at 100.0° C comes into contact with a block of aluminum at 20.0°C. The final temperature of the blocks is 60.0°C. What are the relative masses of the blocks?


    2. Relevant equations
    mcΔT
    copper specific heat = .386 J/g°C
    aluminum specific heat = .900 J/g°C

    3. The attempt at a solution

    (x)(.386 J/g°C)(40°C) = (x)(.900 J/g°C)(-40°C)
    what I use to try to find the mass, assuming that the energy lost in one part of the system is gained by the other.... Also, what is meant by "relative" mass in this question?

    Until I realize this equation cannot be solved...

    Any help is appreciated not really sure how to go about doing this problem, I feel like Im missing something because this should be very easy.
     
  2. jcsd
  3. Mar 6, 2014 #2

    tiny-tim

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    Science Advisor
    Homework Helper

    Hi Ritzycat! :smile:
    I think they mean: what is the ratio of the two masses (ie what is one mass relative to the other).

    (imo, this is not a correct use of the words "relative masses" :redface:)
     
  4. Mar 6, 2014 #3
    Thanks for the response.

    If the question is referring to ratio, wouldn't the ratio of their masses simply be the ratio of the specific heat capacities? (given the absolute value of delta T is the same)
     
  5. Mar 7, 2014 #4
    What can you say about the heat loss/gain of each block?
     
  6. Mar 8, 2014 #5

    Borek

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    Staff: Mentor

    Only if you can prove it. Just write heat balance using [itex]m_{Al}[/itex] and [itex]m_{Cu}[/itex] and solve for [itex]\frac {m_{Al}} {m_{Cu}}[/itex].
     
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