How do we come to know that a chemical reaction has taken place?
Answer:
The presence of any of the following changes helps us to determine that a chemical reaction has taken place.
- Formation of new substance(s)
- Change in state
- Change in colour
- Change in temperature
- Formation of a precipitate
- Evolution of a gas
For example, if on mixing two substances a gas is evolved, then we can say that a chemical reaction has taken place.