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Isothermal compression of monatomic gas ?

  1. Sep 29, 2003 #1

    zaf

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    Hello forum members

    I need some help on H.W problem...just enough reasoning to atleast get started

    the question is as follows:
    5 moles of a monoatomic ideal gas at an initial volume of .50 m^3 and an initial pressure of 2.0 * 10^5 Pa undergoes an isothermal compression to .20m^3. Find the final pressure ?

    so, the temperature is going to be constant , the inital and final volumes and intial pressure is also know, also the total energy (Q)is going to be work done on the gas... which must be negaive... internal energy is conserved ? am i correct so far....how do i solve this ?
     
  2. jcsd
  3. Sep 29, 2003 #2

    Njorl

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    Science Advisor

    You're overcomplicating. The energy doesn't figure into it. It is also irrelevant that the gas is monatomic. The problem is much easier than you suspect.


    Njorl
     
  4. Sep 29, 2003 #3
    Right Njorl,
    all there is to use is the equation of an ideal gas:
    pV = nRT.
    Since there is initial & final state, it's a system of 2 equations:
    I) p1V1 = nRT
    II) p2V2 = nRT
    Now, T is not given, so you better eliminate it:
    I) T = p1V1/nR
    II) T = p2V2/nR
    Which are clearly equal, so
    I = II) p1V1/nR = p2V2/nR
    or (nR cancels)
    p1V1 = p2V2
    And we solve for p2:
    p2= p1V1/V2
    OK?
     
  5. Sep 29, 2003 #4

    Njorl

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    Yes, but I thought it should be left for Zaf to do with just the hint.

    Njorl
     
  6. Sep 29, 2003 #5

    zaf

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    yes. i understand arcnets... thank you
     
  7. Sep 30, 2003 #6
    Yes, right. Maybe that was a little too much...
     
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