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How much heat ΔQ is consumed to raise the ice temperature

  1. Dec 8, 2011 #1
    1. How much heat ΔQ is consumed to raise the ice temperature from Ti = -20 Celsius to meltingpoint Tf = 0 ? how long does it take ?



    2. dQ/dt = H = 300 W

    dQ = cmΔT




    3 I got it to be 2.49 * 10^-21 J. Is it right ?
     
  2. jcsd
  3. Dec 8, 2011 #2

    Andrew Mason

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    Re: Heat/Energy

    You will have to provide a bit more information. How much ice are we talking about? Does the heat source provide 300 W?

    AM
     
  4. Dec 9, 2011 #3
    Re: Heat/Energy

    I dont know anything about the mass.

    c = 1/m * dQ/dt (1)

    c = 4190 kJ/kg (heat capacity of water)

    Q = mcΔT (2)

    From equation (1): m = (dQ/dt)/c (3)

    m = 300W/4190 k//kg = 0.0715 kg

    (2) Q = (0.0715 kg)(4190 kJ/kg)(273-15-253.15)K <==>

    Q = 5.99 =~ 6 J

    t = Q/H (4) (heat/power)

    t(time) = 6.0 J/300 W = 0.02 J/s = 2 min

    Is it right ?
     
  5. Dec 9, 2011 #4
    Re: Heat/Energy

    How did you get the equation (1)?
     
  6. Dec 9, 2011 #5
    Re: Heat/Energy

    I just solved it, an oversight
     
  7. Dec 9, 2011 #6

    Andrew Mason

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    Re: Heat/Energy

    The units are wrong. c has units of energy/mass. 1/m(dQ/dt) has units of energy/(mass x time).

    Your derivation of m makes no sense. You are using the wrong heat capacity. You have to use the heat capacity of ice, not liquid water. Are you sure you got it solved?

    AM
     
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