How can you tell that the product of the reaction is different from the iron that began the reaction?

The product of the reaction can be identified as different from the original iron by observing changes in physical and chemical properties. For example, the product may exhibit a different color, texture, or state (solid, liquid, gas) compared to the metallic iron. Additionally, chemical tests can reveal new properties, such as reactivity or solubility, that were not present in the initial iron. These changes indicate that a chemical transformation has occurred, resulting in a substance distinct from the original iron.