Changes that do not alter the chemical composition of a substance are called what type of changes?

Changes that do not alter the chemical composition of a substance are referred to as physical changes. In these types of changes, the substance may undergo transformations such as changes in state (like solid to liquid, liquid to gas), size, shape, or appearance, but its internal structure and chemical identity remain the same. For example, melting ice into water is a physical change; though the form of water is different, it remains H2O chemically.

In contrast, chemical changes involve a transformation that alters the chemical structure of a substance, resulting in new substances being formed. Biochemical changes specifically pertain to processes involving living organisms, which often include biochemical reactions that change the substances involved. Thermal changes generally refer to changes caused by temperature variations, which may cause physical changes but do not exclusively define them. Thus, the definition of physical changes aligns perfectly with the notion of maintaining the chemical composition of a substance.