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Thermodynamics entropy problem

  1. Sep 21, 2009 #1
    1. The problem statement, all variables and given/known data
    Find (a) the energy absorbed as heat and (b) the change in entropy of a 2.00 kg block of copper whose
    temperature is increased reversibly from 25°C to 100°C. The specific heat of copper is 386 J/kg K .


    2. Relevant equations

    dS=dQ/T
    dS=nRln(final volume/initial volume) **for an ideal gas**

    3. The attempt at a solution\

    Well I got the first part. The energy is just
    dQ=cmdT
    which is (386)(2)(75K)= 57900J

    however, when i got to the second part, I didn't know what to do since the copper isn't an ideal gas, and it has a non-constant temperature so I can't use the first equation. Any help would be appreciated!!!
     
  2. jcsd
  3. Sep 21, 2009 #2
    Entropy Thermodynamics problem

    1. The problem statement, all variables and given/known data

    Find (a) the energy absorbed as heat and (b) the change in entropy of a 2.00 kg block of copper whose
    temperature is increased reversibly from 25°C to 100°C. The specific heat of copper is 386 J/kg K .

    2. Relevant equations

    dS=dQ/T
    dS=nr ln(vf/vi) **for an ideal gas**

    3. The attempt at a solution

    The first part was relatively easy. I just used the equation:
    dQ=cmdT
    so, dQ=(386)(2)(75)=57900 J

    But for the 2nd part, I dont know what to do because copper is not an ideal gas, ruling out the 2nd equation, and the temperature is not constant, meaning I cannot use the first equation. Any help would be great!!!
     
  4. Sep 21, 2009 #3
    Re: Entropy Thermodynamics problem

    dS = dQ/T
    dQ = cmdT
    dS = cmdT/T
    Integrate both sides to get delta(S) = cm*ln(Tf/Ti); be sure to use Kelvin.
    Its been a while since I've done thermodynamics, so I might be wrong...though I only applied a bit of mathematical procedure, so it seems as though it would be fine.
     
  5. Sep 21, 2009 #4
    Re: Entropy Thermodynamics problem

    sounds right to me.... thanks for the help!
     
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