You can know if a chemical reaction has taken place by looking for several key indicators:
- A color change occurs that is permanent and not reversible.
- The production of a gas , often visible as bubbles (effervescence).
- The formation of a solid precipitate from liquids.
- A noticeable temperature change , either heat absorbed or released.
- Sometimes a change in odor or a reaction producing sound (e.g., an explosion) can be observed.
These signs indicate that new substances have been formed with different chemical properties than the starting materials, confirming that a chemical reaction has occurred.
