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Calculate CO concentration at high altitude

  1. Jun 12, 2014 #1
    Question:
    You are cooking in a tent at 17,000ft with outside air temp at -15F. The concentration of CO in the tent is 40ppm. Calculate the equivalent CO concentration in mg/m^3.

    First, I converted 17000ft to atm and got 501.5atm, which seems very wrong.

    Next, I converted -15F to 247.039K.

    I applied the Ideal Gas Law, PV=nRT

    I tried to solve for V.

    p=501.5 atm
    n(molecular weight CO)=28
    R (should be a constant)=.082056
    T=247.039

    I come up with a ridiculous answer. It seems simple, but I can't figure out where I'm going wrong.
     
  2. jcsd
  3. Jun 12, 2014 #2
    Forgot to mention also, (but it's obvious) that the conditions are not at STP. (not 25C, not 1.0 atm)
     
  4. Jun 12, 2014 #3
    Show us how you calculated the pressure at that altitude?

    Chet
     
  5. Jun 12, 2014 #4

    SteamKing

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    Why do you think altitude is equivalent to atmospheres? Your calculation assumes that there is a water column 17000 feet tall somewhere.

    FWIW, this calculation is OK.

    Well, for one thing thinking that the atmospheric pressure at 17000 feet altitude is 500 atmospheres. (Hint: the atmospheric pressure decreases with altitude, although not in a linear relationship.)
     
  6. Jun 13, 2014 #5

    SCP

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    Check your units. At 17,000 ft, atmospheric pressure should be ~500 kPa, or 0.5 atm. If the answer you're getting is off by 3 orders of magnitude, this might be why.
     
  7. Jun 13, 2014 #6

    D H

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    So why didn't you stop right there?

    It obviously is very wrong. When you get an answer that seems very wrong, you should stop and double check. Carrying a bad calculation forward is generally a very bad idea because that bad calculation oftentimes poisons all subsequent results.


    That's wrong, too. One atmosphere is on the order of 100 kPa, so 500 kPa is about 5 atmospheres.
     
  8. Jun 13, 2014 #7

    SteamKing

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    It's that damn metric system confusin' everyone again.
     
  9. Jun 16, 2014 #8

    SCP

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    Ah yes. I was thinking in millibars. Silly. In any case, at 17,000 ft you should get pressure at ~0.5 atm (or ~50 kPa).
     
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