What distinguishes a physical change from a chemical change?

A physical change is characterized by alterations in the physical properties of a substance, such as its shape, size, or state (solid, liquid, gas), without changing its chemical composition. For instance, when water boils, it changes from a liquid to a gas, but the chemical structure of H2O remains unchanged. This key principle highlights that the substance after the change retains its original identity.

In contrast, chemical changes involve a transformation that results in the formation of one or more new substances with different chemical compositions. An example of a chemical change would be the rusting of iron, which undergoes a reaction with oxygen to form iron oxide, a completely new substance.

Options that imply conditions or limitations, such as chemical changes occurring only in gases or that physical changes may create new substances, do not accurately describe the fundamental distinctions between the two types of changes. The focus on temperature change as a characteristic of chemical changes is also misleading, as temperature changes can occur during both types of changes. Thus, the distinction lies in the preservation of the substance's composition during physical changes, making the first choice the accurate descriptor.