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Heat capacity questions query

  1. Apr 29, 2010 #1
    hey for this question
    If a 2kg sample of aluminium absorbs 64.4 kJ of heat from its surrounds by how much does its temperature increase

    the answer is 65.1

    how? i got 32.5
    q=mcT
    T=q/mc=(64.6x10^3)/(2000x.9930)

    also same for this question
    If 0.5g of an organic compound is completely combusted in air in a constant press calorimeter with a heat capacity of 510 J K-1 a temperature rise of 5.9 degrees is recorded. The heat of combustion (kJ g-) of the compound is approximately

    the answer is 3009...
    i convered C to c then used q=mcT
    which gave me 3009 J , so shouldnt it be 3.00 kJ
    so 3.00/0.5 to get kJ per gram
     
  2. jcsd
  3. Apr 30, 2010 #2

    Borek

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    Staff: Mentor

    To some extent you are twice right (that is assuming specific heat of Al is 0.9930). Although details are fuzzy at best.

    Can you elaborate on

    You mean you converted 5.9 to 5.9?

    And what did you put for m?
     
  4. Apr 30, 2010 #3
    Yeah where did you get the mass lol.
     
  5. May 2, 2010 #4
    Cheers for the reply guys,
    Um, i meant C as in heat capacity and c as in specific heat (c=C/m)
    the mass was given as 2kg
     
  6. May 2, 2010 #5

    Borek

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    Staff: Mentor

    Show precisely what you did and how, as as far as I can tell you did something else. You should use heat capacity of the calorimeter to calculate amount of heat (and numbers show that's what you did), not specific heat. And if you calculated specific heat - specific heat of what, and what have you used for mass (c=C/m)?
     
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