What defines a chemical change?

A chemical change is characterized by a transformation where substances are converted into new substances with distinct chemical properties. This process means that the molecular structure of the original substances undergoes a modification, resulting in substances that have different chemical compositions and characteristics. For example, when you burn wood, it reacts with oxygen to form ash, carbon dioxide, and water vapor—new substances that possess unique properties compared to the original wood.

The other options describe processes that may involve changes in appearance or state but do not capture the core aspect of a chemical change, which is the formation of new substances. Changes that alter physical appearance or involve reversible processes maintain the original substances’ chemical composition and are not chemical changes. Hence, the focus on the transformation into new substances with different properties is what distinctly defines a chemical change.