1. Evidence of Chemical Reactions
Unit 5

2. How do you know a chemical reaction has occurred?
Unlike a physical change, where no substances are created, a chemical change creates new substances by rearranging atoms.
Law of Conservation of Mass –states that during a chemical reaction, mass is neither created nor destroyed.

3. Evidence of a Chemical Reaction
Precipitation – a solid is created.

4. Evidence of a Chemical Reaction
A gas evolves

5. Evidence of a Chemical Reaction
Formation of water-

6. Evidence of a Chemical Reaction
Changes in energy to the system
It gets colder
It gets hotter