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Thermodynamic Problem HELP

  1. Aug 12, 2009 #1
    1. The problem statement, all variables and given/known data

    The problem is on the attachment. I cant seem to find the volume or temperature of T. If someone can tell me how to find them i can do the rest of the problem. Any help would be greatly appreciated.

    2. Relevant equations



    3. The attempt at a solution

    on the attachment
     

    Attached Files:

  2. jcsd
  3. Aug 12, 2009 #2

    kuruman

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    You say you can't seem to find the volume or temperature. What have you tried? What equations did you start from?
     
  4. Aug 12, 2009 #3
    i used the PV= NRT

    I cant find the Volume and Temperature of point C only.
     
  5. Aug 12, 2009 #4

    kuruman

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    I will not be able to offer any suggestions until I can open your attachments.
     
  6. Aug 12, 2009 #5
    Well the problem is

    One mole of a diatomic ideal gas has a pressure of 8atm and a volume of 3 L at point A. The gas is then expanded isothermally to point B where the volume is 12 L. The gas is then compressed isobarically to point C. the gas is returned to point A via an adiabatic compression. Depending on the calculation assume that R is 8 J/Mol (K) or .08 L atm/ mol K
     
  7. Aug 12, 2009 #6

    kuruman

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    I can see the attachments now. You are given the volume, pressure, number of moles and R. Can you find the temperature at point A?
     
  8. Aug 12, 2009 #7
    yes i found the temp of A and B because they are the same since they are isothermal. knowing that i could find the Pressure of B and C because they are isobaric, but i cant find the volume or temp of point C.
     
  9. Aug 12, 2009 #8

    kuruman

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    OK. Now there is an equation that relates point A to point B and one that relates point A to point C. What are these equations?
     
  10. Aug 12, 2009 #9
    I dont know what equations and how do they relate? by going back to a via adiabatic process doenst that mean no heat is transferred?
     
  11. Aug 12, 2009 #10

    kuruman

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    Yes, adiabatic means no heat is transferred. Also, for the adiabatic process,

    pAVAγ = pCVCγ

    where γ = CP/CV

    Find γ for a diatomic gas, then use this relation to find VC.
     
  12. Aug 12, 2009 #11
    so Cp/Cv= 7/2R divided by 5/2R? where R is .08?
     
  13. Aug 12, 2009 #12
    and then what do i do? can you show me please?
     
  14. Aug 12, 2009 #13
    i get y= 1.4 then what do i do?
     
  15. Aug 12, 2009 #14

    kuruman

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    Use the relation I gave you earlier to find VC. You know everything else. Once you have VC, you can find TC.
     
  16. Aug 12, 2009 #15
    i get Vc^1.4= 42.8 how do i solve that? can anyone else help?
     
  17. Aug 12, 2009 #16
    Surely you know logarithms?
     
  18. Aug 12, 2009 #17
    is it ln 42.8= 1.4? but then what do i solve?
     
  19. Aug 13, 2009 #18

    kuruman

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    You can rewrite 1.4 as 7/5. You get

    VC7/5=42.8

    Raise both sides of the equation to the 5/7 power. This gives you

    (VC7/5)5/7=42.85/7

    Can you get a number for VC now?
     
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