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Homework Help: Equilibrium Question

  1. Jun 12, 2010 #1
    1. The problem statement, all variables and given/known data

    1 mol of each of the following gases is set up with the reaction K=4

    IBr + Cl2 <-> ClBr + ICl

    Find the final concentration of ClBr

    2. Relevant equations

    k= products/reactants

    3. The attempt at a solution

    First find Q to be 1 by finding the molarity of each gas to be 1/4 M/L. Q<K Therefore equilibrium must shift to right. Set up ICE table as follows:

    4 = (1/4+x)2

    x= 3.75?

    nvm x should be = 0.15. Calculation mistake.
    Last edited: Jun 12, 2010
  2. jcsd
  3. Jun 13, 2010 #2
    Hi Hockeystar!
    Maybe it is easier to thing of the problem the following way: in the beginning you had 1 mol of each gas, then as K=4 some amount of reagents is used up and more of the products are formed.
    If x mol IBr and x mol of Cl2 reacted to form more products then at equilibrium the amounts of gases will be these: 1+x mol of ICl and BrCl, and 1-x mol of IBr and Cl2, thus
    K=(1+x)^2/(1-x)^2=4, x=0,33 (mol).
  4. Jun 13, 2010 #3
    But I thought when calculating Ksp the products and reactants must be molarity, not moles?
  5. Jun 14, 2010 #4
    Actually it depends on the temperature of the reaction vessel. My assumption was that all the reactants and products are gaseous and thus it wouldn't matter whether you take molarities or quantities, because volumes cross out anyway.
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