K=...? (pg 73 course reader pre-equilibrium ex)

[Zoe Robertson 2H]

Hi!
For the pre-equilibrium example on page 73, the fast step is: NO + NO <==> N2O2. Then K is written as: K=[N2O2]/[NO]^2
I'm confused why N2O2 is in the numerator, because of the formula K1=k1/k1*. Isn't the reverse equilibrium reaction k1*?
I thought it would be flipped. Thanks!

[Michelle_Li_1H]

Hi!
That K would be the equilibrium constant, which would equal to the concentration of the products over the concentration of the reactants.

The purpose is to find an equation that relates the intermediate or in this case [N2O2] with [NO]^2. We would do so by treating the first step as if it were at equilibrium, which gives us the equilibrium constant K.

Hope this helps!