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Homework Help: Basic equilibrium problem

  1. May 6, 2008 #1
    1. I am having trouble figuring out how to work the most basic equilibrium problem when there is an initial concentration of reactants only and no product. How am I supposed to find the constant with a zero in my quotient? Here is an example problem:
    At 527˚C, K = 0.0160 for the following reaction: 2HI(g) ↔ H2 (g) + I2 (g)
    What is the equilibrium concentration of H2
    if the initial concentrations of both H2 and I2
    = 0.0160 M and the initial concentration of
    HI = 0 M?

    2. k = product/reactant

    3. If I knew where to start I wouldn't need help
  2. jcsd
  3. May 6, 2008 #2
    What will happen to your system if you know that the rxn must be at equilibrium, but it is not currently at equilibrium?
  4. May 6, 2008 #3


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    Science Advisor
    Homework Helper

    You mentioned that K=[product]/[reactants] - write this equation out in full detail and remember that they refer to the equilibrium values.
  5. May 7, 2008 #4
    one way of solving this problem is by breaking it into parts.

    initially, [H2] = [I2] = 0.0160 mol/dm3
    [HI] = 0 mol/dm3

    at equilibrium, let [HI] be x mol/dm3
    then, accordingly, [H2] = [I2] = {0.0160 - (x/2)} mol/dm3, because 2 mol HI are produced by using 1 mol H2 and 1 mol I2.

    find the equilibrium constant in term of x.
    and then solve for x by equation the above expression to 0.0160
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