1. Energy and Chemical Reactions
Physical Science
Chapter 10.2 Part 1

2. Our Story So Far Discuss with your partner, discuss with the class…
What is a chemical reaction?
What are some things you might observe when a chemical reaction occurs?
Explain how to tell if a chemical equation is balanced?
Explain how to balance a chemical equation.

3. Use of Energy in Reactions
Energy used to break bond between elements in a compound
Energy is released when new bonds form

4. Exothermic Reactions
New bonds release more energy than it took to break the old bonds
3Fe(s) + 2O2(g) Fe3O4(s)

5. Endothermic Reactions
Forming new bonds generates less energy then it took to break the original bonds
6CO2 + 6H2O  C6H12O6 + 6O2
Photosyntesis

6. Activation Energy Needed to start a reaction and break chemical bonds
If you don’t have activation energy, you don’t have a reaction
If you don’t need activation energy, the reaction has already happened.

7. Addition Reactions Aka Synthesis reactions
Two or more substances come together to form a different compound
4Fe + 3O2  2Fe2O3
Polymerization is an addition reaction the builds long chains or polymers
Acid rain is a addition reaction

8. Decomposition Reaction
A single compound breaks down to form two or more substances
2NaHCO3  CO2 + Na2CO3 + H2O
A word about notation (s) means solid, (l) means liquid, (g) means gas, (aq) means a solution
2NaHCO3(s)  CO2(g) + Na2CO3(s) + H2O(l)

9. Activity Continue to work on balancing chemical equations packet.
Due at end of class