[roldy]

I need to calculate what the partial pressures are for the species in air in chemical equilibrium at 0.1 ATM and 4500 K. This problem is part of a bigger problem. The species present in air are O₂, O, N₂, N (NO is ignored). The equilibrium constants of O₂ and N₂ are given.

K_p,O2=12.19 ATM
K_p,N2=0.7899*10^-4 ATM

Here's is my work (my logic might be wrong)

(1)   P_O2 + P_N2 + P_O + P_N=0.1

X_O2M_O2 + X_N2M_N2 + X_OM_O + X_NM_N=M_air

But X_i=P_i/P, so now the mass equation becomes
(P_O2/P)M_O2 + (P_N2/P)M_N2 + (P_O/P)M_O + (P_N/P)M_N=M_air

rewriting and plugging in the masses for each species
I said that the mass of air contains 20% O₂ and 80% N₂. Thus, M_air=.2(32) + .8(28)=28.8.

(2)   32P_O2 + 28P_N2 + 16P_O + 14P_N=28.8(.1)=2.88

Mole fraction:

N_O^initial/N_N^initial=N_O^final/N^final=(2n_O2 + n_O)/(2n_N2 + n_N)

so rewriting,

(3)   2P_O2 - .5P_N2 + P_O - .25P_N=0

With the reactions,
O₂ :rarrow:2O
N₂ :rarrow:2N

I know that,
K_p,O2=P_O²/P_O2
K_p,N2=P_N²/P_N2

Thus,

(4)   P_O=sqrt(K_p,O2*P_O2)

(5)   P_N=sqrt(K_p,N2*P_N2)

It would seem that all I need to do is to substitute eq(4) and eq(5) into eq(1) - (3). However these are nonlinear due to the sqrt terms. Is my method correct? Where did I mess up?

[SABRY]

You have 4 unknowns and 4 equations. Should be able to solve.

The 4 equations are:
Equations (1), (2) and the 2 equilibrium relationship.

[roldy]

I figured it out. Thanks for the reply though.