Kp Partial Pressures @ equilibrium?

Question

Equilibrium problem? how can i set this up? I tried the typical initial, change , and equilibrium table, but i keep getting it wrong.

1 atm of N2 and 3 atm of H2 are mixed at 500Celcius to produce 2.12atm of NH3, find Kp for the reaction.
2NH3<->N2 + 3H2

I see how you got that, but i dont think this is the right answer, isnt the pressures given for H2 and N2 the initial values? don't we use equilibrium values to get Kp? It seems to me that the 500Celcius is important, maybe some sort of ideal gas law issue?

Answer 1

Let p1 = partial pressure of N2
p2 = part. press of H2
p3 = part press of NH3

From the reaction given, the coefficient of NH3 = 2, the coefficient of N2 = 1 and the coefficient of H2 = 3

The equilibrium equation is

Kp = (p3)^2/[((p2)^3)*(p1)]

Kp = 0.17