according to the reaction equation:
by using ICE table:
CO(g) + Cl2(g) ↔ COCl2(g)
initial 0.025 0.0035 0
change -X -X +X
Equ (0.025-X) (0.0035-X) X
when:
Kp = P(COCl2)/P(CO}*P(Cl2) when Kp= 0.2
by substitution:
0.2 = X / (0.025-X)(0.0035-X) by solving this equation for X
∴ X = 1.74x10^-5