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Required heat, entropy change of object dropped in water

  1. Mar 2, 2016 #1
    1. The problem statement, all variables and given/known data
    A 1 liter container is filled with argon to pressure of 10^5Pa at 303K. Dropped into pool at temp 323K. How much heat is needed to heat the gas to 323K? what is the entropy change in the gas and the universe? ignore the entropy change in container.

    2. Relevant equations
    c_v=3/2*R
    dq=cdt
    deltaS=integral of dQ/T

    3. The attempt at a solution
    I started with the entropy:

    reservoir:
    T is constant so delta Q/ T_R = C(T_s-T_r)/T_r = 0.77. negative sign because its entropy reduced.
    system:
    evaluating the same integral with a non constant T gave me C*ln(T_r/T_s) = 0.79.
    Universe:
    change in the universes entropy was 0.02 after adding both of these together.

    I'm unsure of these answers and at first I figured I should just use C(T_s-T_r) to find the heat added but the question mentions the initial pressure and the constant volume of 1 litre so I think im missing something.
    Thanks
     
  2. jcsd
  3. Mar 2, 2016 #2
    I figured I needed to find n so I calculated n to be 0.04 from pV=nRT.
    Does this mean I should have had n before C in the entropy parts too?
     
  4. Mar 2, 2016 #3
    Yes. You've done great.
     
  5. Mar 2, 2016 #4
    thank you sir
     
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