Final answer:
A sign that a chemical change has occurred includes the emission of sound and heat, which are indications that new substances with different chemical properties are being formed.
Step-by-step explanation:
A sign that a chemical change has happened is usually observed through changes that cannot easily be reversed. Examples of such changes include:
- Temperature changes: the substance either gets warmer or cooler, indicating a chemical reaction is occurring.
- Light emitted: light can be given off during chemical reactions, as seen when something burns.
- Color changes: an unexpected change in color can indicate a new substance has been formed.
- Bubbles: bubbles are formed when a substance is undergoing a chemical reaction that produces a gas, and not just boiling.
Out of the options provided, sound and heat are signs of a chemical change. These are evident in processes such as the burning of gasoline, which produces heat, light, and new substances like carbon dioxide and water vapor.
Additional examples of chemical changes include the souring of milk or the burning of a candle, both resulting in the formation of new substances with different chemical properties. Contrarily, a physical change, such as the melting of ice to water, does not result in different substances but merely a change in state.