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Homework Help: Adiabatic Expansion?

  1. Apr 23, 2005 #1
    An ideal monatomic gas, consisting of 2.47 mol of volume 0.0890 m^3, expands adiabatically. The initial and final temperatures are 22.3oC and -64.3oC. What is the final volume of the gas

    According to a formula in the book, the volume of an ideal monatomic gas' volume expands by 1.52, but I think I am misinterpreting that. Anyway, I have tried using the formula

    V2/ V1 = (P1/P2)^y -- but I don't know how to get the second pressure. Any help would be appreciated.
     
  2. jcsd
  3. Apr 23, 2005 #2
    Can You express P through V and T? From ideal gas equation.
     
  4. Apr 23, 2005 #3
    PV = nRT ?
     
  5. Apr 23, 2005 #4
    Yes. You know that P*V^(gamma) is constant!? So P1*V1^gamma=P2*V2^gamma
    But V=V(P,T). Thus, You can find any function depndent on V and T which is constant. it will be like V*T^(q), where q is any coefficient which can be expressed with gamma
     
  6. Apr 23, 2005 #5
    wait, can you try that again, I don't get what you're saying, sorry.
     
  7. Apr 23, 2005 #6
    You have PV = nRT. n and R are constant.
    You also know V2/ V1 = (P1/P2)^y (do You understand what is y?)
    From other angle P1/P2 = (T1*V2)/(T2*V1) (From ideal gas equation), isn't it?
    So, know You can express T1/T2 through V1/V2.
     
  8. Apr 23, 2005 #7
    No, I don't understand y
    It says that y = Cp/Cv -- and then it lists values for real gasses, but this is a general gas

    I see what you're saying for the second part, I guess I just am frustrated with looking at it.
     
  9. Apr 23, 2005 #8
    As You have written "V2/ V1 = (P1/P2)^y", y =Cv/Cp. Usually is used gamma = Cp/Cv=1/y. did You get the answer?
     
  10. Apr 23, 2005 #9
    Yeah, its gamma, I just don't know how to put gamma on the computer. Anyway, no, I am still very confused. Don't worry about it, I'll try to solve it, I guess I just don't know where to get started with all of these formulas. Thanks for the help though.
     
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