How is a physical change distinct from a chemical change?

A physical change is distinct from a chemical change primarily because it involves alterations to the form or state of a substance without affecting its chemical composition. Reversible processes are often characteristic of physical changes; for instance, melting ice into water can be reversed by freezing the water back into ice. This ability to revert to the original state without altering the fundamental chemical identity of the substance highlights the key distinction.

In contrast, chemical changes involve a transformation that alters the chemical composition of the substances involved. For example, when hydrogen gas reacts with oxygen to form water, new substances are created that cannot be easily separated back into the original reactants. The option suggesting physical changes are irreversible misrepresents the nature of many physical changes, such as phase changes, which are indeed often reversible. The claim that a chemical change occurs only at high temperatures is misleading, as chemical reactions can occur at various temperatures, not solely elevated ones.