Final answer:
Physical changes do not alter the identity of a substance, while chemical changes result in the formation of new substances. Observations such as color change, temperature change, light emission, and the formation of bubbles or precipitates can indicate a chemical change.
Step-by-step explanation:
Chemists make a distinction between two different types of changes that they study-physical changes and chemical changes. Physical changes are changes that do not alter the identity of a substance. On the other hand, chemical changes occur when one substance is turned into another substance.
Observations that indicate a chemical change has occurred include color change, temperature change, light given off, formation of bubbles, and formation of a precipitate. These indications can help scientists determine if a chemical reaction is taking place.