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Homework Help: Gas Laws

  1. Dec 2, 2005 #1
    1) A combustion cylinder (containing a fixed number of moles of gas initially at 9.00atm ) with a moveable piston is maintained at a constant temperature changes volume from 2.00 L to 6.0 L. Determine the change in pressure during this action.

    P1 = 9.00 atm
    V1 = 2.00 L
    P2 = ?
    V2 = 6.0 L

    Use P1V1 = P2V2, where P2 = (P1*V1)/(V2) = (9.00atm*2.00L)/(6.0 L) = 3.0 atm??

    delta P (change in P) = P2 - P1 = 3.0 atm - 9.00 atm = -6.0 atm?? (correct significant digits?)

    2) A combustion cylinder (containing a fixed number of moles of gas initially with a pressure of 4.00atm ) with a fixed piston changes temperature from 9.00 kelvin to 4.00 kelvin. Determine the change in pressure during this action.

    P1 = 4.00 atm
    T1 = 9.00 K
    P2 = ?
    T2 = 4.00 K

    Use P1/T1 = P2/T2, where P2 = (P1*T2)/(T1) = (4.00 atm)(4.00 K)/(9. 00K) = 1.7778 atm??

    Change in pressure (delta P) = P2 - P1 = 1.78 atm - 4.00 atm = -2.22 atm???

    Thank you for any help.
     
  2. jcsd
  3. Dec 2, 2005 #2
    i think it is ok as i don't see any mistakes.
     
  4. Dec 3, 2005 #3

    lightgrav

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    Homework Helper

    The only thing to worry about is whether your gas CONDENSES as it cools to 4 Kelvin. At such low Temperatures, almost nothing acts like an IDEAL gas.
     
  5. Dec 4, 2005 #4
    Well, exactly what formula/method would you use if it wasn't an ideal gas?
     
  6. Dec 4, 2005 #5

    Pengwuino

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    Gold Member

    Well if he was not given any more information, you must assume it uses the ideal gas law... you would need experimental values otherwise i believe.
     
  7. Dec 4, 2005 #6

    kp

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    use the Van Der Waals equation for real gases.
     
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