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Ideal gas temperature/pressure/volume problem

  1. Sep 25, 2014 #1
    1. The problem statement, all variables and given/known data
    A mass of gas at an initial pressure of 38 bar, and with an internal energy of 1400kJ, is contained in a perfecty insulaed cylinder of volume 0.06 meters cubed. the gas is allowed to expand behind a piston until its internal energy is 1300kJ. the law of expansions is PV^1.8=C. find:
    work done
    the final volume
    the final pressure


    2. Relevant equations
    PV^1.8=c
    Uinital + Q = U final + W
    W = (PiVi - PfVf)/(n-1)
    PiVi^1.8=PfVf^1.8


    3. The attempt at a solution
    Ui - Uf = W - Q
    1400-1300= W - 0
    1000 = W
     
  2. jcsd
  3. Sep 27, 2014 #2

    ehild

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    Homework Helper
    Gold Member

    Welcome to PF!


    Your equation for the work is not correct. The work of the gas when it expands from volume Vi to volume Vf is equal to the integral [tex] W=\int _{V_i}^{V_f}{PdV}[/tex]

    In case of this gas, [tex]P = \frac{P_iV_i^{1.8}}{V^{1.8} }[/tex]


    1400-1300=100 kJ

    ehild
     
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