how to get concentrations of all species

Question

Kp for the reaction O3(g) = NO3(g) <=> O2(g) = NO2(g) is 6.0x10^20 at 450 c. if 2.00 moles of oxygen and 2.00 moles of nitrogen dioxide are placed into a 10.00 liter vessel at 450 c what will be the equilibrium concentrations of all species

Answer 1

For these types of problems, it is useful to set up an ICE table.  See below.

I do believe you have written the reaction incorrectly.  Perhaps you meant the following:

O₃(g) + NO(g) <==> NO₂(g) + O₂(g)

0..........0...................2.00.........2.00.......I

+x.......+x.................-x.............-x...........C

x..........x...............2.00-x.......2.00-x......E

 

So, at equilibrium (E), the concentration of O₃  and NO = x and that of NO₂ and O₂ = 2.00-x.  Plug these values into the K_c equation

K_c = [NO_2][O₂]/[O_3][NO]  and solve for x which gives you [O₃] and [NO].  Subtract the value of x from 2.00 to get [NO₂] and [O₂]. However, since you are given K_p at 450ºC, and NOT K_c, you should use the relationship that K_c = K_p/(RT)^Δn where R = universal gas constant, T= temperature in K and )Δn = change in number of moles, which in this case is zero since the balanced equation shows 2 moles on the left and 2 moles on the right.