 Okay, so let's try this one, useless at least principle on this equation. Phosphorus dried chloride plus chlorine gas goes to phosphorus pentachloride plus heat. Since we have heat here as a product, we know it's an exothermic reaction. If heat was over here, it would be an endothelic reaction. So if we add PCL5 or phosphorus pentachloride, that's a product, so if we're adding it, it's going to push the equilibrium to the left. If we add a reaction or Cl2, it's going to push the equilibrium away from it, it's going to push it to the right. We take PCL5, which is a product, and remove it, it's going to push the equilibrium to the right. Temperature decreased, okay, since it's an exothermic reaction, temperature decreasing means that we're removing heat. Since it's an exothermic reaction, heat is a product, so if we remove it, it's going to push it to the right, push it to the product side. And the catalyst, the catalyst doesn't do anything to the equilibrium. It only affects the rate at which the reaction occurs, so if you add a catalyst to the reaction, no equilibrium shift will occur.