You go on vacation for a week and leave a bowl of fruit on the table. When you return you observe the pieces of fruit. What clues would indicate that the fruir has undergone a chemical change?
Mostly odor, also perhaps a color change.
The indicators of a chemical change are: gas produced (sometimes you can smell it), unexpected color change, formation of another substance, and a temperature change. Te fruit would have begun to rot or get overripe, producing a gas that you can smell. It may also have changed color (bananas are a good example).