What type of change occurs when iron rusts?

When iron rusts, it undergoes a slow chemical change. This process involves the reaction of iron with oxygen in the presence of moisture, forming iron oxide, commonly known as rust. During this transformation, the chemical properties of the iron change fundamentally; it does not merely alter its shape or appearance as would occur in a physical change.

The rusting process is characterized by its gradual nature, taking place over time as iron continues to react with atmospheric oxygen and water. This is a clear indication of a chemical change, as new substances are created (iron oxide) with different properties than elemental iron. Understanding that rusting is a chemical reaction helps clarify why it is designated as a slow chemical change rather than a physical one or an instantaneous reaction.