- A chemical change involves a chemical reaction where one or more substances are transformed into different substances with different properties. - Burning is a combustion reaction where paper reacts with oxygen, producing ash, carbon dioxide, water vapor, and other substances. This process forms new chemical compounds and is not easily reversible. - Physical changes alter the form or appearance of a substance but not its chemical composition. Magnetization, dissolution, and phase changes (like freezing water) are physical changes, as the original substances retain their chemical identity and the process is often reversible.