1. Forming New Substances
Chapter 9 - 1

2. Chemical Reactions
A chemical reaction is a process in which one or more substances change to make one or more new substances.
The chemical and physical properties of the new substance are different from the original substances. + =

3. Signs of Chemical Reactions
Some reactions form precipitates, which are solid substances in a liquid.
Some other signs include gas production, color change, and energy given off in the form of light, heat, or electrical energy.

4. A Change of Properties
The most important sign of a chemical reaction is the formation of a new substance.
The properties of these new substances are very different from those of the starting substances.

5. Bonds: Holding Molecules Together
A chemical bond is the force that holds two atoms together in a molecule.
For a chemical reaction to take place, the original bonds must break and new bonds must form.

6. Breaking and Making Bonds
Step #1: Starting substances break apart.
Step #2: The atoms rearrange.
Step #3: New bonds form.

7. Reactions and Energy
Energy is needed to break chemical bonds in chemical reactions.
As new substances form, energy is released or absorbed.

8. Exothermic Reactions
A chemical reaction in which energy is released is called an exothermic reaction.
Exo means “go out” or “exit.”

9. Endothermic Reaction
A chemical reaction in which energy is taken in is called an endothermic reaction.
The energy that is “taken in” is absorbed from the surrounding area, leaving it cold.

10. The Law of Conservation of Energy
The law of conservation of energy states that energy cannot be created or destroyed.
However, energy can change form and it can be transferred from one object to another.