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Homework Help: Thermodynamics PV Diagram

  1. Sep 29, 2003 #1


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    Hello forum members

    I have a HW problem on ploting a P-V digram, I worked out a solution..can someone have a look at it and let me know if I am correct

    the Question is as follows

    2 moles of a monatomic ideal gas initially occupies a volum of 100 liters at a pressure of 100 KPa. The gas then expands iobarically to 200 liters (leg 1->2), followed by an isometric pressure increase to 300 KPa (leg 2-3), and ending in an isobaric expansion to 300 liters (leg 3->4).

    Find change in U (internal energy) for each leg
    Find W (work) for each leg
    Find Q (heat exchange) for each leg

    here is part of the solution

    T1 = (100000 * .10) / (8.314 * 2) = 601 K
    U1 = (3/2)*2*8.31*601 = 14982 J

    T2 = (100000 * .20) / (8.31 * 2) = 1203 K
    U2 = (3/2)*2*8.31*1203 = 29990 joules

    U for leg 1->2 is +15008.79 joules

    W for leg 1-2 would be 10000 joules, which is P times change in volume

    Am i correct so far...if that is so...then i can solve the rest

  2. jcsd
  3. Oct 2, 2003 #2

    Its a while since i did this, but i think thats correct. I got dU by using dU = nCdT = 2 * 12.47 * 602 = 15014 J which is close enough.

    Your method for working out the work is correct i think, i also got 10,000 J

    What is isometric? i know of isobaric (const pressure), isochoric (const volume), isothermic (const temp), but isometric ive not heard of..

    I presume isometric means isochoric?
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