1. Formation of a new substance with different properties: This is the most fundamental indicator. If a chemical change occurs, the original substances are transformed into something entirely new, with different physical and chemical properties. For example, burning wood changes it into ash, carbon dioxide, and water, none of which have the same properties as the original wood.

2. Production of heat or light: Chemical reactions can release or absorb energy in the form of heat (exothermic or endothermic reactions) or light (chemiluminescence). Think about the heat and light produced by a campfire or the glow of a firefly.

3. Production of gas bubbles: The formation of gas bubbles is a sign that a new substance is being produced, which is often a gas that is escaping from the reaction mixture. For example, when baking soda is added to vinegar, carbon dioxide gas is produced, resulting in the fizzing you observe.

Keep in mind that these are just common indicators, and there may be other signs of a chemical change depending on the specific reaction.