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Homework Help: Gas Equilibria

  1. Feb 5, 2009 #1
    1. The problem statement, all variables and given/known data
    The Equilibrium constant for A(g) -> 2B(g)
    is 1x10^-2 at 1000k. Calculate the fraction on A which is dissociated at 1000k if the total pressure is
    1 atm
    10^-3 atm

    2. Relevant equations
    PV=nRT
    B^2 / A = Ke (1x10^-2)

    3. The attempt at a solution
    for A PV=1x8.714x1000 = 8.714x10^3
    for B PV=2x8.714x1000 = 17.428



    All i can work out from this is that theres gunna be a 1:2 ratio? Im completely lost and my minds gone blank. Thanks in advance for the help
     
  2. jcsd
  3. Feb 5, 2009 #2

    Borek

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    Staff: Mentor

    Solve in terms of partial pressures. What is sum of pA and pB?
     
  4. Feb 5, 2009 #3
    surely it would be pA+2pB=1atm ?
    and im not very sure how to solve in terms of partial pressures

    would i have
    kp= pB^2 / pA
    so 0.01 = pB^2 / pA

    I've tried using a simultaneous equation with pA+2pB=1
    and just end up with rubbish
     
  5. Feb 5, 2009 #4

    Borek

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    Staff: Mentor

    Why pA + 2 pB? Do you know definition of partial pressure?
     
  6. Feb 5, 2009 #5
    because there's 2 moles of it? i thought that was right, my bad.

    pA+pB=1atm that right?
    would i be right to use a simlt equ then?
     
  7. Feb 5, 2009 #6

    Borek

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    Staff: Mentor

    2*yes.
     
  8. Feb 5, 2009 #7
    ok using the equations i end up with the quadratic:
    pB^2 + 0.01pB-0.01=0 so pB=0.095atm
    so pA=0.905atm
    and i can work out for the other atm


    thanks
     
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