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Homework Help: Where Did I Mess Up In Solving This?

  1. Apr 25, 2013 #1
    1. The problem statement, all variables and given/known data
    For the reaction: A + B ↔ C + D

    6.0 moles of A and 5.0 moles of B are mixed together in a suitable container. When equilibrium is reached, 4.0 moles of C are produced.

    The equilibrium constant for this reaction is:

    a. K = 1/8
    b. K = 8
    c. K = 30/16
    d. K = 16/30

    2. Relevant equations


    3. The attempt at a solution

    I set up the problem like this:

    Initial Concentrations: [A] 6/x 5/x [C] 0 [D] 0

    Change in Concentrations: [A] -4/x -4/x [C] +4/x [D] 0

    Equlibirum Concentrations: [A] 2/x 1/x [C] 4/x [D] 0

    I assigned the variables x myself:
    x= volume of container

    The reason I put 0 for D's concentration is b/c the problem did not say any amount of D was formed.

    Therefore the equilibrium expression should look like this:
    which further equates to 2x. I don't where I messed up or how to solve this. Any help would be appreciated. Thanks.
  2. jcsd
  3. Apr 25, 2013 #2
    Well if 4 moles of C are produced, how many moles of D are produced? Also, if if it were 0, then you would find that the equilibrium constant is zero by the formula for K and you could not just ignore it.
  4. Apr 25, 2013 #3
    oh....duh *hits forhead*. Thanks so much. How silly of me to overlook that.
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