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Homework Help: Hard molar specific heat question?

  1. Nov 4, 2012 #1
    1. The problem statement, all variables and given/known data
    At very low temperatures, the molar specific heat of many substances varies as the cube of the absolute temperature: C=k*(T^3/To^3),
    which is sometimes called Debye's law. For rock salt, To= 281K and k= 1940 J/mol*K

    Determine the heat needed to raise 2.40 mol of salt from 30.0K to 50.0K .



    2. Relevant equations
    I don't know if this equation applies to solid . Q=nC*ΔT


    3. The attempt at a solution
    I know ΔT is 20, it seems to me that the only unknown for this question is T.
    I tried to plug in 30 OR 50 into T, but I got the wrong answer.
     
  2. jcsd
  3. Nov 4, 2012 #2

    Borek

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    Staff: Mentor

    Q=nCΔT is OK, but to make things more difficult C is a function of temperature.
     
  4. Nov 4, 2012 #3
    Could you tell me how to get the C value for this question? I know C=k*(T^3/To^3) from the problem, it also gives me k and To value, but I don't know what is T value.
     
  5. Nov 4, 2012 #4

    Borek

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    Staff: Mentor

    T is given in the problem and is not constant - it changes from 30 to 50 K. You need to integrate.
     
  6. Nov 4, 2012 #5
    It works!!!!!!I just need to integrate that C function, thank you!!!
     
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