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Homework Help: Chemical Equilibrium Problem

  1. Sep 15, 2010 #1
    1. The problem statement, all variables and given/known data
    At a certain temperature, the equilibrium constant for the gaseous reaction of CO with O2 to produce CO2 is 5000 lit/mole. Calculate [CO] at equilibrium, if 1 mol each of CO and O2 afre placed in a 2 L vessel and allowed to come to equilibrium.


    2. Relevant equations



    3. The attempt at a solution

    Concentration at equilibrium
    CO= 1-x
    O2= 1-x/2
    CO2=x where x is the no of moles dissociated

    Kc=x^2/(1-x)^2(1-x/2)=5000

    I dont understand what assumption I should make to solve this.
    answer is [CO]= 0.014
     
  2. jcsd
  3. Sep 15, 2010 #2

    Borek

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    Staff: Mentor

    I have not tried to solve, so it is possible there will be some more hurdles, but first step is more or less obvious - equilibrium is shifted far to the right, so amount of product is almost stoichiometric.

    I have a gut feeling that it will be better to approach the question from the other end - assume you started with 1 mole of CO2 and half mole of oxygen. x will be very small then and approximations will be much more obvious.
     
    Last edited by a moderator: Aug 13, 2013
  4. Sep 15, 2010 #3
    As you said I took 1 mole CO2 and half mole O2
    and got x value as 0.058 (moles of CO)
    But how do we relate this the problem (1 mole CO and 1 mole O2)
     
  5. Sep 15, 2010 #4

    Borek

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    Staff: Mentor

    Through stoichiometry. If total amount of substances present is identical, it doesn't matter if you start with products or reactants, equilibrium is the same.
     
    Last edited by a moderator: Aug 13, 2013
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