when we have this equation:
CO(g) + Cl2(g) ↔ COCl2(g)
intial 0.147 0.175 0
change -X -X +X
final (0.147-X) (0.175-X) X
so from the ICE table, we substitute in Kc formula :(when we have Kc = 255)
Kc = [COCl2]/[CO][Cl2]
255= X / (0.147-X)(0.175-X)
255 = X / (X^2 - 0.322 X + 0.025725)
X = 0.13
∴[CO] = 0.147 - X = 0.147 - 0.13
= 0.017 m