Phosgene (Cl2CO), a poison gas used in World War I, is formed by the reaction of Cl2 and CO. The proposed mechanism for the reaction is
Cl2 ⇌ 2 Cl (fast, equilibrium)
Cl + CO ⇌ ClCO (fast, equilibrium)
ClCO + Cl2 → Cl2CO + Cl (fast)
What rate law is consistent with this mechanism?