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Understanding Energy Changes in Chemical Reactions

This resource explores the energy changes during chemical reactions, focusing on identifying exothermic and endothermic reactions. Students will learn to classify reactions based on energy flow and understand the law of conservation of energy. Key examples include the combustion of propane and the melting of butter, illustrating practical applications of energy concepts. Through independent practice and homework assignments, learners deepen their understanding of chemical energy and the nature of bond formation and breaking in reactants and products.

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Understanding Energy Changes in Chemical Reactions

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

  2. 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.

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

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

  5. Energy in or out? Breaking bonds Forming Bonds

  6. Bonds, Chemical Bonds

  7. 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.

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

  9. 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.

  10. Exothermic reaction

  11. Exothermic Reaction Example Heat is on the _____ side

  12. Endothermic reaction

  13. Endothermic Reaction Example Heat is on the _____ side

  14. All together now

  15. 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

  16. 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

  17. 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

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