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Specific Heat of Alcohol

  1. Jan 27, 2010 #1
    1. The problem statement, all variables and given/known data

    A mass of 200 grams of copper, whose specific heat is 0.095, is heated to 100° C, and placed in 100 grams of alcohol at 8° C contained in a copper calorimeter, whose mass is 25 grams, and the temperature rises 28.5°C. Find the specific heat of the alcohol.

    2. Relevant equations

    ΔH=cmΔT
    C=H/mΔT

    3. The attempt at a solution
    The heat of placing the copper into the calorimeter is the energy used to warm the alcohol via conduction. We first have to decide how much heat it takes to raise the temp of the alcohol from 8° to 28.5°.
    Use equation:
    ΔH=cmΔT = (0.095)(200g)(100-0)
    Since no beginning heat is given, we will assume the copper was heated from 0°C.
    = 1,900 J

    Knowing the force of heat energy that heats the alcohol, we can then rearrange the equation to find the specific heat of alcohol:
    C=H/mΔT = 1,900/(100g)(28.5-8) = 0.93 J/g.K


    Am i on track here?
     
  2. jcsd
  3. Jan 27, 2010 #2

    rl.bhat

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    Heat lost by the copper = mc*cc*(T1 - T) where T is the final temperature of the mixture.
    Heat gained by the alcohol along with calorimeter is
    (mc*cc + ma*ca)(T - T2) where T2 is the initial temperature of the alcohol.
     
  4. Jan 27, 2010 #3
    i understand now we need to find the the heat gained by the calorimeter to find the total energy for the final part of the equation but there are still components missing.

    1)how much heat is lost by the copper:
    ΔH=cmΔT = (0.095)(200g)(100-28.5).
    = 1,358.5 J

    2)how much heat is gained by alcohol and calorimeter
    (25)(cc) + (100)(ca) (28.5-8)

    Then Ca = Heat Gained - Heat Lost/mΔT

    but how do you find cc and ca for part 2?
     
  5. Jan 27, 2010 #4

    rl.bhat

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    In [(25)(cc) + (100)(ca)] (28.5-8)
    cc is the specific heat of the calorimeter which is given. And ca is the specific heat of alcohol which you have to find out.
     
  6. Jan 27, 2010 #5
    So we don't have to do this: Then Ca = Heat Gained - Heat Lost/mΔT first right?

    In In [(25)(cc) + (100)(ca)] (28.5-8)
    i dont' think the specific heat of the calorimeter is given - the specific heat of the copper is given. Would you use:

    (25)(0.092) + (100)(CA)(20.8) = 0
     
  7. Jan 27, 2010 #6

    rl.bhat

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    (0.095)(200g)(100-28.5) = [(25)(0.095) + (100)(CA)](20.8)

    Note the bracket.
     
    Last edited: Jan 27, 2010
  8. Jan 27, 2010 #7
    almost there i think
    1358.5 = [2.375 + (100)(ca)] (20.8). i ge tthis but if you solve this for ca=.629
    We're looking for the "heat gained" value not ca in this equation. how do you find the heat gained value from the above equation to solve the one below?
    [Ca = heat Gained - Heat Lost]/mΔT first right
     
  9. Jan 27, 2010 #8

    rl.bhat

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    "We're looking for the "heat gained" value not ca in this equation."
    Heat gained by the alcohol and calorimeter is equal to heat lost be the water.
    And in the problem they have asked to find the specific heat of the alcohol.
     
  10. Jan 27, 2010 #9
    If heat gained is equal to heat lost then the value would be 1358.5.
    When you set the equation like this don't you have to solve for ca? it's the only unkown.
    1358.5 = [2.375 + (100)(ca)] (20.8)

    and if heat gained is equal to heat lost then the numerator of our equation will be 0 right?
    Ca = heat Gained - Heat Lost]/mΔT first right
     
  11. Jan 27, 2010 #10

    rl.bhat

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    "Ca = heat Gained - Heat Lost]/mΔT"
    From where did you get the above expression? This is wrong.
     
  12. Jan 27, 2010 #11
    Oh i thought that was the final step. So if heat gained equaled heat lost then heat gained would be 1358.5 J. And
    1358.5 = [2.375 + (100)(ca)] (20.8)
    Ca = .629 ?
     
  13. Jan 27, 2010 #12

    rl.bhat

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  14. Jan 27, 2010 #13
    Thank you! :)
     
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