Energy Changes in Reactions

1. Energy Changes in Reactions Physical Science December 7, 2011 Ms Cilli Pages 206-209

3. Objectives • Describe the energy changes that take place during chemical reactions. • Classify chemical reactions as exothermic or endothermic. • Explain how energy is conserved during chemical reactions.

4. What type of reaction is this? C3H8 + 5O2  3CO2 + 4H2O

5. What is chemical energy? • Chemical Energy: • Chemical reactions involve the ________ of bonds in the reactants and the ________ of bonds in the products.

6. Energy in or out? Breaking bonds Forming Bonds

7. Bonds, Chemical Bonds

8. Remember Phase Changes?!?! Is heat lost or gained? 1. A plastic bottle of water is placed in a freezer. After several hours, the water has frozen solid. 2. A chef places a stick of solid butter in a saucepan, and heats the saucepan over low heat on a stove. After several minutes, the stick of butter has melted.

9. Will you either come in or go out? Exothermic: Endothermic:

10. Is heat lost or gained? Exothermic or Endothermic? 1. A plastic bottle of water is placed in a freezer. After several hours, the water has frozen solid. 2. A chef places a stick of solid butter in a saucepan, and heats the saucepan over low heat on a stove. After several minutes, the stick of butter has melted.

11. Exothermic reaction

12. Exothermic Reaction Example Heat is on the _____ side

13. Endothermic reaction

14. Endothermic Reaction Example Heat is on the _____ side

15. All together now

16. Tale of Two Reactions Is it endothermic or exothermic? (Look and ask yourself what side the heat is on) C3H8 + 5O2 3CO2 + 4H2O + 2220kJ 2HgO + 181.7 kJ  2Hg + O2

17. Closure…onestepcloser Which one is not one of the 5 types of chemical reactions? • synthesis • decomposition • single-replacement • double-replacement • All of these are chemical reactions

18. Assignment: • Independent Practice: • Read section 7.3 • Work on the study guide • Homework: • Complete the section 7.3 HW • Due Thursday, December 8 by 8PM