Forming New Substances

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 newsubstances. • The chemical and physical properties of the new substance aredifferentfrom 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 importantsign of a chemical reaction is the formation of a newsubstance. • The properties of these new substances arevery 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 originalbonds must break and newbonds must form.

6. Breaking and Making Bonds • Step #1: Starting substances break apart. • Step #2: The atomsrearrange. • 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 exothermicreaction. • Exo means “go out” or “exit.”

9. Endothermic Reaction • A chemical reaction in which energy is taken in is called an endothermicreaction. • 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 conservationof energy states that energy cannot be created or destroyed. • However, energy can change form and it can be transferred from one object to another.

11. THE END • LET’S TRY IT!