Final answer:
A chemical change occurs when bonds between atoms or molecules are broken and formed, creating a different substance with new properties. Indicators of a chemical change include temperature change, light emission, unexpected color changes, and formation of bubbles.
Step-by-step explanation:
What is a Chemical Change?
A chemical change is a type of change that occurs when bonds are broken and formed between molecules or atoms, transforming one substance with a set of properties into a different substance with different properties. A notable characteristic of chemical changes is that they are often more challenging to reverse than physical changes. For instance, when a paper burns, the paper (cellulose) chemically reacts with oxygen to form carbon dioxide, water, and ash, which are completely different substances from the original paper and oxygen.
Indicators of Chemical Change
Several observations can indicate that a chemical change has occurred:
- A temperature change, which can be an increase or decrease in temperature unrelated to external heat sources.
- Light emission may occur without obvious reasons such as electricity or fire.
- Unexpected color changes suggest that new substances are forming with different properties.
- Formation of bubbles indicating a gas is produced during the reaction.
These signs help chemists and students understand when a chemical reaction is taking place, as opposed to simply a physical change where the substance's fundamental composition remains unchanged.