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Homework Help: Chemical Equilibrium

  1. Aug 15, 2007 #1
    1. The problem statement, all variables and given/known data
    The following reaction initially contains [A]o = 0.2150 M and o = [C]o = 0.4150 M. If the equilibrium constant for the reaction is Keq = 2.03, what are the concentrations of reactants and products when the reaction has achieved equilibrium? What is the value of deltaG for the reaction at 25oC?

    2 A <-> B + C



    2. Relevant equations

    I am stuck as on how to proceed with the math. I'm not sure if I am doing it correctly or not. Could someone please take a look?


    3. The attempt at a solution

    Initial: 2A B C
    0.2150M 0.4150M 0.4150M

    Change: +x -x -x
    Since Q>Kc, as Qc = [C]/[A]^2

    Equil. 0.2150+x 0.4150-x 0.4150-x

    I'm stuck on the whole rearranging and solving for x bit. I know I'm supposed to use quadratic formula.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Aug 15, 2007 #2

    chemisttree

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    Gold Member

    Substitute the values you know for the equilibrium concentration of A, B and C (A=0.2150+x, B=0.4150-x, C=0.4150-x) into the expression for equilibrium and solve it.

    Keq=2.03=[(0.4150-x)^2/(0.2150+x)^2] and expand it out, multiply both sides by (A+x)^2, do the algebra until the expression for Keq is in the form:

    0 = ax^2 + bx + c (note that here the terms a, b and c are not the same as A, B and C given in the problem)

    Hint: The first step should look like this:

    2.03*(0.2150+x)^2 = (0.4150-x)^2, after multiplying both sides by (0.2150+x)^2
     
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