When iron filings are mixed with sulfur powder and the mixture is heated, a black substance called iron sulfide is formed. Which statement best describes the changes involved?

When the mixture of iron (Fe) and sulfur (S) is heated, they undergo a chemical reaction to form a new substance, iron (II) sulfide (FeS). Unlike a physical mixture, the new compound (FeS) has entirely different properties from its constituents. For example, iron is magnetic, but iron sulfide is non-magnetic and cannot be separated using a magnet. A chemical change is typically irreversible by simple physical means. You cannot recover the original iron filings and sulfur powder once they have reacted to form the black, solid mass of iron sulfide. The reaction is exothermic, meaning it releases heat energy once the initial heating starts the process, often causing the mixture to glow.