What property distinguishes a chemical change from a physical change?

A chemical change is distinguished from a physical change primarily by the formation of a new substance. In a chemical change, the original substances undergo a transformation, resulting in the creation of new substances with different chemical properties. For instance, when iron rusts, it reacts with oxygen in the air to form iron oxide, which is a different substance than iron and oxygen themselves. This process alters the chemical identity of the materials involved.

In contrast, physical changes do not lead to the production of new substances; they might alter the form or state of the substance, such as melting ice to water, but the chemical composition remains the same. Understanding this distinction is crucial, as it helps in identifying reactions and processes in various applications, from industrial operations to everyday life.