Which statement best describes a chemical change?

• A. Creates a new substance
• B. Only changes state
• C. Reversible only
• D. Involves only physical properties

Answer: (A)

A chemical change is when matter changes into a new substance with a different chemical identity. That’s exactly what happens when a new substance forms, with its own unique formula and properties. For example, burning wood produces ash and gases, which are not the same substances as the original wood.

Physical changes, by contrast, only affect how a substance appears or exists (like changes in state or shape) without changing what the substance is chemically. Melting ice, for instance, is still water, just in a different phase. Reversibility isn’t the defining feature of a chemical change—some chemical changes are hard or impossible to reverse, while others can be reversed under certain conditions. Likewise, chemical changes involve changes in chemical properties and composition, not just physical properties.