What defines a chemical change?

A chemical change is characterized by a process that results in the formation of one or more new substances. This transformation involves breaking and forming chemical bonds, leading to different chemical properties than those of the original substances. An example of this is the rusting of iron, where iron reacts with oxygen to create iron oxide, a new substance that has different properties than elemental iron.

The focus on the creation of new substances is what distinguishes chemical changes from other types of changes, like physical changes. While a physical change might alter the appearance, state, or shape of matter without modifying its chemical identity, a chemical change fundamentally changes the materials involved. This is why a change that produces one or more new substances is the definitive hallmark of a chemical change, highlighting the transformation at the molecular level.