1. Formation of a new substance: This is the most fundamental indication of a chemical change. The properties of the new substance are different from the original substances.
* Example: Burning wood produces ash, carbon dioxide, and water - all substances different from the original wood.
2. Change in color: A chemical change can often result in a distinct color change.
* Example: The browning of an apple after being cut is a chemical change that results in a color change.
3. Production of gas: The formation of bubbles or the release of a gas is a strong indicator of a chemical change.
* Example: Baking soda and vinegar react to produce carbon dioxide gas.
4. Production of heat or light: Chemical reactions can release or absorb heat (exothermic or endothermic reactions). Light may also be emitted, such as in a combustion reaction.
* Example: A burning candle releases heat and light.
5. Formation of a precipitate: A precipitate is a solid that forms from a solution during a chemical reaction.
* Example: When you mix solutions of lead nitrate and potassium iodide, a yellow precipitate of lead iodide forms.
6. Change in odor: The formation of a new substance can often result in a new, distinct odor.
* Example: Sour milk has a different odor than fresh milk due to chemical changes that have occurred.
Important Note: Not all of these indicators will be present in every chemical change. However, the presence of one or more of these indicators strongly suggests that a chemical change has taken place.
