The equilibrium constant is given for one of the reactions below. Determine the value of the missing equilibrium constant.

H2 (g) + Br2 (g) ⇌ 2 HBr (g) Kc = 3.8 * 104

4 HBr (g) ⇌ 2 H2 (g) + 2 Br2 (g) Kc = ?

To calculate Kc of the second step, we must observe the first reaction.

If we rotate the first reaction and multiplay it by 2 we get the same thing.

So the rotation means 1/kc (first reaction)

And by multiplying it by 2, K should be squared.

Kc2=1 / (kc1) ^2=6.92*10^-10