Chemistry
posted by K .
Determine Kc for the following reaction:
1/2N2(g) + 1/2O2(g)+ 1/2Br(g) <> NOBr(g)
from the following information (at 298K)
2No(g) <> N2(g) + O2(g) Kc = 2.1x10^30
NO(g) + 1/2Br2(g) <> NOBr(g) Kc = 1.4

Take equn 1, divide by 2, and reverse it. That makes Kc of 2.1E30 = k' [1/(sqrt 2.1E30)]. That is sqrt because you took 1/2 the equation and the reciprocal because you reversed it.
Then add eqn 2 and check to see that it is the equation you want. K for the final rxn is k'*k2 = 1.4/(sqrt 2.1E30) = ?? 
Thank you so much. I got 9.7 x 10^16. The answer is correct. I was just confused because why did we only substitute the k values for 2 compounds in the equation rather then all 4?