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Pressure equilibrium -- I am getting my math wrong somewhere

  1. Dec 6, 2015 #1
    1. The problem statement, all variables and given/known data
    The equilibrium constant, Kp, for the following reaction is 0.636 at 600 K:

    COCl2(g) CO(g) + Cl2(g)

    Calculate the equilibrium partial pressures of all species when COCl2(g) is introduced into an evacuated flask at a pressure of 1.73 atm at 600 K.

    2. Relevant equations
    Included below

    3. The attempt at a solution
    The equilibrium constant, Kp, for the following reaction is 0.636 at 600 K:

    COCl2(g) CO(g) + Cl2(g)

    Calculate the equilibrium partial pressures of all species when COCl2(g) is introduced into an evacuated flask at a pressure of 1.73 atm at 600 K.

    PCOCl2=
    PCO=
    PCl2=

    setting up ICE, I know that Kp=x/(1.73-x)=.636

    (.636)[1.73-x]^2=x
    (.636)[1.73^2-2(1.73)x + x^2]=x
    (.636)x^2-[2(1.73)(.636)+1]x + (.636)(1.73)^2

    x^2-[2(1.73)+1/(.636)]x + 1.73^2= 0

    a=1
    b= -[2(1.73)+1/(.636)]= -5.032
    c= (1.73)^2= 2.993

    quadratic equation such that:
    [(-5.032)^2-4(2.993)]^1/2 = [13.349]^1/2= 3.654

    x=(-(-5.032)+-3.654)/2
    x=4.343 or .689

    Go with .689 since the other value of x is greater than the initial pressure of 1.73.
    PCO=PCL2=(1.73-x)=(1.73-.689)=1.041
    PCOCL2=x=.689
     
  2. jcsd
  3. Dec 7, 2015 #2

    Borek

    User Avatar

    Staff: Mentor

    Already doesn't look correct to me.
     
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