Phosgene, COCl2 (g), is an extremely toxic gas. It was used during World War I. Today it is used to manufacture pesticides, pharmaceuticals, dyes, and polymers. It is prepared by mixing carbon monoxide and chlorine gas.
CO (g) + Cl2 (g) = COCl2 (g) <-- the equal sign should be the sign for foward and reversible reactions ( arrows facing both ways )
An ICE Problem is solved in detail.