Discuss reaction of zinc and hydrochloric acid to produce a gaseous product. Determine that it involves both a physical and chemical change. The physical change was the change of the solid zinc a soluble solute, and the chemical change involved the production of a gaseous product, hydrogen. Discuss some physical and chemical reactions, like the electrolysis of salt to produce a soft metal and a green gas. Write the formulas for sodium chloride solution reacting with silver nitrate solution to produce the photographic precipitate silver chloride which is used in the manufacturing of film.