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Homework Help: Concentration of nitrogen oxide in air

  1. Oct 13, 2013 #1
    1. The problem statement, all variables and given/known data

    The relative compositions of the pollutants NO and NO2 in air are governed by the reaction

    NO + 1/2 O2 ⇔NO2

    For air containing 21-mol% O2 at 25C and 1.0133 bar, what is the concentration of NO in parts per million if the total concentration of both nitrogen oxides is 5 ppm? Note ppm is taken on a molar basis for gases.

    2. Relevant equations

    3. The attempt at a solution

    For this problem I am not sure how to go about it. I am not 100% sure if ppm means moles/total moles. Also, I am not able to find out the concentration of NO2 at equilibrium, which is why I haven't been able to get the concentration of NO.

    Attached Files:

  2. jcsd
  3. Oct 14, 2013 #2


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    Staff: Mentor

    My chem study is too long ago to be able to help you. But I think I'd be looking for some sort of equilibrium constant at that temp & pressure, to be able to relate the proportion of moles of NO2 to NO. Do you have that?

    Have you tried a google search? Often you can find a worked example on which you can base your approach.
  4. Oct 14, 2013 #3

    rude man

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    Homework Helper
    Gold Member

    Pose this in the chemistry section of PF.
  5. Oct 15, 2013 #4
    In this context, ppm means mole fraction times 1 million.
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