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Homework Help: Pressure, Volume and Temp Change WORK done?

  1. May 19, 2012 #1
    Pressure, Volume and Temp Change...WORK done???

    n = 9.95 moles of an ideal gas are slowly heated from initial pressure P1 = .922 atm and initial volume V1 = 679 L to final pressure Pf = 1.16 atm and final volume Vf = 1073 L. Find T1, the initial temperature of the gas. If the plot of this process on a P-V diagram is a straight line, find W, the work done on the system.

    P1 = .922 atm x 1.013 x 10^5 Pa = 93398.6 Pa
    V1 = 679 L / 1000 = .679 m^3

    PV = nRT
    (93398.6)(.679) = (9.95)(8.314)(T)
    T = 767 K

    For the Work done I would just need to find the area under the curve for the P-V diagram...correct? Well that is what I did and my answer is considered wrong and I cannot understand why...

    When V = .679 m^3, P = 93398.6 Pa. And when V = 1.073 m^3, P = 117508 Pa. The area of the rectangle under the curve is (1.073 - .679) x 93398.6 = 36799.0484 J. The area of the triangle under the curve is 1/2bh = (.5)(1.073-.679)(117508 - 93398.6) = 4749.5518 J

    So W SHOULD = 36799.0484 + 4749.5518 = 41548.6002 J = 41.5 kJ...but this is considered WRONG....Can someone please advise what I am doing wrong?? Very frustrated here!!
     
  2. jcsd
  3. May 19, 2012 #2

    ehild

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    Homework Helper

    Re: Pressure, Volume and Temp Change...WORK done???

    Check the sign of work. The work done on the system was asked.

    ehild
     
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