250 mol nocl was placed in a 250 l reaction vessel at

Question

2.50 mol NOCl was placed in a 2.50 L reaction vessel at 400ºC. After equilibrium was established, it was found that 28% of the NOCl had dissociated according to the equation

2NOCl(g)    2NO(g) + Cl₂(g).

Calculate the equilibrium constant, K_c, for the reaction.

Step 1: 2.50mol / 2.50L = 1.0M

Step 2: 1.0-28%=0.72

After that I'm not sure what to do.