There are several signs that can indicate a chemical reaction has taken place:
1. **Color Change**: A noticeable change in color can suggest a chemical reaction, such as when a solution becomes brighter or darker.
2. **Temperature Change**: A reaction may release or absorb heat, causing a change in temperature. This may result in the mixture feeling warmer or cooler to the touch.
3. **Gas Production**: The formation of gas bubbles or fumes is