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Homework Help: Gas Laws

  1. Jun 20, 2007 #1
    1. The problem statement, all variables and given/known data
    A 200g sample of CO2 occupies a volume of 110 L at a pressure of 1 atm.

    a) What is the number of moles in the gas

    b) What is the temperature?

    c) if the volume is increased up to 200 L and the temperature is kept constant. what is the new pressure.


    2. Relevant equations



    3. The attempt at a solution
    a) 110/24.7 = 4.45 ( i think thats right)

    b) pV = constant is that constant the temperature???

    if so the temperature = 1 x 110 = 110

    c) ( p1 v1 ) / T1 = ( p2 V2 ) / T2

    (1 x 110) / 110 = ( p2 x 200) / 110

    p2 = (1 x 110 x 110) / (110 x 200) = 0.55


    i'm not sure if i'm doing this right can anyone help?

    THANKS!
     
  2. jcsd
  3. Jun 20, 2007 #2

    G01

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    For part a)

    I'm sorry, but I don't understand what you're doing here. HINT: How many grams in one mole of CO2?

    For Part b)

    I think you're thinking of the Ideal Gas Law. If so, that is:

    [tex]PV=nRT=NkT[/tex]

    where n=number of moles, R=gas constant, N=number of molecules, k=Boltzman's constant.

    If you can do the above, then you should get part c) right, since your method above was correct.

    Good Luck!
     
    Last edited: Jun 20, 2007
  4. Jun 20, 2007 #3

    Chi Meson

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    A) how about a few units? What is "24.7" here?

    b) no, not at all.

    c) 0.55 whats? ATM here, despite having the wrong temperature.

    EDIT: BLAST! beaten again by GO1 !
     
  5. Jun 20, 2007 #4

    G01

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    Heh! Sorry Chi, I'm just quick and sneaky like that!
     
  6. Jun 20, 2007 #5
    ok well the ratio of CO2 is

    12:32

    one mole of C is 6.02x10^23 x 12

    one mole of O is 6.03x10^23 x 16

    but how do i work out how much of the 200g is carbon?

    thanks so far!
     
  7. Jun 20, 2007 #6
    ok scrap that last post lol,

    1 mole of carbon-12 is 12 grams,
    1 mole of oxgen-16 is 16 grams,

    so i still need to know how much of the 200g is carbon.

    thanks
     
  8. Jun 20, 2007 #7

    Dick

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    CO2 is a molecule consisting of one atom of carbon and two of oxygen. So one mole of CO2 is one mole of C plus two moles of O.
     
  9. Jun 20, 2007 #8
    oh ok, so does that mean that the number of moles in 200g of CO2 is

    0.2 (kg) / (6.02 x 10^32)

    all x 3 becuase there are 3 moles per molecule
     
  10. Jun 20, 2007 #9

    nrqed

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    What is the mass of one mole of CO2? (you already gave the mass of one mole of C and of O so that will be easy.

    Once you have the mass of one mole of CO2, you simply have

    number of moles of CO2 = 200 gr/(mass per mole of CO2)
     
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