q.1 why liquid br2 reacts slowly as compared to vapours of bromine? Think about collision theory. Gas molecules possess more kinetic energy than molecules as a liquid. Gases thus have a larger frequency of collisions and, additionally, are more likely to possess sufficient energy to overcome repulsive forces, (\(i.e. E_a\)). These factors contribute to a greater likelyhood of a successful collision that results in chemical reaction.