hydrochloric is a kind of acid & a limestone is put into a hydrochloric acid solution & limestone is made of calcium carbonate ->  putting a limestone in hydrochloric is similar to putting calcium carbonate into acid  putting a limestone in hydrochloric is similar to putting calcium carbonate into acid & calcium carbonate reacting with acid produces carbon dioxide ->  limestone reacting with hydrochloric acid will produce carbon dioxide  limestone reacting with hydrochloric acid will produce carbon dioxide & chemical reactions cause new substances to form -> a chemical reaction has taken place between limetone and hydrochloric