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Homework Help: Specific heat/thermal capacity

  1. Feb 16, 2012 #1
    1. The problem statement, all variables and given/known data
    A saucepan of thermal capacity 500J/degC contains 5kg water at 20 degrees celcius. How much energy is required to raise the temperature of the saucepan and water:
    a) to 60 degrees
    b) by 60 degrees

    2. Relevant equations
    Q = mcΔt
    mcΔt = mcΔt

    3. The attempt at a solution
    First I just did Q = 5 * 500J * 40 = 100 000J, but then I realised mcΔt = mcΔt possibly had to be used. Please help get me on the right track asap! :)
  2. jcsd
  3. Feb 16, 2012 #2
    You need to know the SHC of water to calculate the heat energy required for the water.
    You are given enough information to calculate the heat energy required by the pan.
  4. Feb 16, 2012 #3
    So would it be 2 separate answers for a, 100 000J for the water and 840 000J for the pan?
    Or would it be 500*5*(60-T) = 4200*5*(60-20)
    Or does the correct method derive one answer... I'm seriously lost .-.
  5. Feb 16, 2012 #4
    You have to calculate the total energy (pan+water) each time
    500*5*(60-20) + 4200*5*(60-20) is correct for part(a)
    Can you see how to do part (b)..... a very subtle difference
  6. Feb 16, 2012 #5
    Are you sure? I was unsure about that because it doesn't account for transferred energy..
  7. Feb 16, 2012 #6
    Thermal capacity is not specific heat capacity
  8. Feb 16, 2012 #7
    Thermal capacity refers to an object, the pan needs 500J to change its temperature by 1C
    Specific heat capacity refers to a substance, water needs 4200J to raise the temp of
    1kg by 1C. Specific means 'per kg'
    I think I have made a mistake in my previous post.... the pan should be 500*(60-20)
    I think that is what Vipho has picked up.... SORRY.... careless.
    Last edited: Feb 16, 2012
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