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Homework Help: Find volume of a mixed gas at STP

  1. Oct 5, 2008 #1
    1. The problem statement, all variables and given/known data
    Consider the following gas phase reaction:
    http://scholar.uh.edu/webct/RelativeResourceManager/Template/Imported_Resources/20053H_CHEM1331_08946_QIZ_200511041405291131475017966%20folder/QIZ_6442871_M/my_files/test_images/f5g1q49g1.gif [Broken]
    400. mL of NO at STP is reacted with 500. mL of O2 at STP. Calculate the volume of the reaction mixture at STP after the reaction goes to completion.

    V of NO= 400.mL= .400L
    V of O2= 500.mL = .500L
    At STP:
    P= 1atm
    T= 273K
    V= 22.4L/mol of gas
    V of mixed gas NO2= ?

    2. Relevant equations

    3. The attempt at a solution
    1, I added two volumes of gases together to get the total volume.
    .400L+.500L= .900L

    2. I calculated the mol of NO2 at STP
    n= PV/RT= (1atm*22.4L)/(0.0821L*atm/K*mol)
    n= 0.9994 mol of NO2

    3. Took that mol multiply with .9L to get the Volume of the mixed gas NO2, I got ~900mL
    But the right answer is 700mL. Is there any idea on what I did wrong?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Oct 6, 2008 #2


    User Avatar

    Staff: Mentor

    The gases reacted. You end with two gases - but you need to calculate their amounts with simple stoichiometry.
  4. Oct 6, 2008 #3
    Thank you! I'll try again!
    Last edited: Oct 6, 2008
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