A Question about Chemical Equilibrium

  • #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:

Answers and Replies

  • #2
James Pelezo
Gold Member
190
58
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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