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A Question about Chemical Equilibrium

  1. Apr 29, 2016 #1
    say we have a reaction:

    N2O4 <====> 2NO2


    for this reaction,if initial number of moles of N2O4 is 'a' can we write

    t = 0 a -
    at equilbrium a-x 2x

    similarly can we do the same for pressure i.e.
    if initial pressure is p,then can we say

    t=0 p -
    at equilbrium p-y 2y

    if yes why? and is x=y,i.e is the number of moles x dissociated equal to decrease in pressure of reactant?
    and is this method valid for all reversible reaction irrespective of the stoichiometric coefficient of reactants and products

    please help.
     
    Last edited by a moderator: Apr 29, 2016
  2. jcsd
  3. May 2, 2016 #2

    James Pelezo

    User Avatar
    Gold Member

    Physics Forums - Equilibrium N2O4(g) <=> 2NO2(g)

    ------------------- N2O4(g) ---- <=> --- 2NO2(g)
    Ci: ------------------ a ------------------------ 0 ---
    ∆C:---------------- -x ---------------------- +2x ---
    Ceq: ------------- a - x -------------------- 2x ---

    Kc = [NO2]2/[N2O4] = (2x)2/(a – x) = 4x2/(a – x) => Kc(a – x) = 4x2 => Kc·a - Kc·x = 4x2

    4x2 + Kc·x + (-Kc·a) = 0

    x = [-b ± (b2 – 4ac)1/2]/2a

    a = 4, b = Kc , c = -Kc·a

    substitute into quadratic; solve for x …

    [N2O4] = a – x

    [NO22] = 2x
     
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