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Notes - Energy & Chemical Change

Notes - Energy & Chemical Change. Chapter 8, Lesson 3. Energy and Chemical Reactions. In chemical reactions, energy is either absorbed or released. In chemical reactions, atoms rearrange. Rearrangement involves some form of energy, usually thermal (heat) energy. thermal energy. light and

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Notes - Energy & Chemical Change

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  1. Notes - Energy & Chemical Change Chapter 8, Lesson 3

  2. Energy and Chemical Reactions • In chemical reactions, energy is either absorbed or released. • In chemical reactions, atoms rearrange. • Rearrangement involves some form of energy, usually thermal (heat) energy. thermal energy light and sound energy

  3. Energy and Chemical Reactions • Some reactions give off light with almost no thermal energy. • Cold light occurs at room temperature.

  4. Energy and Chemical Reactions • Energy is stored in reacting molecules. • The law of conservation of energy states that energy cannot be created or destroyed in chemical reactions. • Energy simply changes from one form to another.

  5. Energy and Chemical Reactions • Molecules have chemical energy stored in their bonds. • Energy is stored in the food that you eat and transferred to your cells.

  6. Net Release of Energy • When atoms rearrange, bonds are broken and new bonds form. • Breaking bonds requires energy. • Forming bonds releases energy.

  7. Net Release of Energy • An exothermic process releases energy in the form of heat. • ex- means “out” • The products in an exothermic reaction have less energy than the reactants.

  8. Net Release of Energy

  9. Net Release of Energy • An endothermic process absorbs energy and feels cooler. • endo- means “in” • The products in an endothermic reaction have a higher energy than the reactants.

  10. Net Release of Energy

  11. Net Release of Energy • Chemical reactions need energy to get started • Activation energy is the minimum amount of energy that has to be added to start a reaction • (i.e.) 2H2 + O2 → 2H2O is an exothermic reaction that needs a spark to get started

  12. Classifying Chemical Reactions • Synthesis Reaction – two or more substances combine to make a more complex substance • A + B → AB • 2 H2 + O2 → 2 H2O

  13. Classifying Chemical Reactions • Decomposition Reaction – a compound reactant breaks down into simpler products • AB → A + B • 2 H2O2 →2 H2O + O2

  14. Classifying Chemical Reactions • Replacement Reaction – one element replaces another in a compound, or two elements in different compounds trade places. • AB + CD → AC + BD • (i.e.) Making pure copper • 2 CuO + C → 2 Cu + CO2

  15. Classifying Chemical Reactions • PracticeClassify each of the following reactions as synthesis, decomposition, or replacement. • 2 NH4NO3 → 2 N2 + O2 + 4 H2O • 2 Al + Fe2O3 → Al2O3 + 2 Fe • MgCl2 + K2S → MgS + 2 KCl • P4O10 + 6H2O → 4 H3PO4

  16. Classifying Chemical Reactions • PracticeClassify each of the following reactions as synthesis, decomposition, or replacement. • 2 NH4NO3 → 2 N2 + O2 + 4 H2O decomposition • 2 Al + Fe2O3 → Al2O3 + 2 Fe • MgCl2 + K2S → MgS + 2 KCl • P4O10 + 6H2O → 4 H3PO4

  17. Classifying Chemical Reactions • PracticeClassify each of the following reactions as synthesis, decomposition, or replacement. • 2 NH4NO3 → 2 N2 + O2 + 4 H2O decomposition • 2 Al + Fe2O3 → Al2O3 + 2 Fe replacement • MgCl2 + K2S → MgS + 2 KCl • P4O10 + 6H2O → 4 H3PO4

  18. Classifying Chemical Reactions • PracticeClassify each of the following reactions as synthesis, decomposition, or replacement. • 2 NH4NO3 → 2 N2 + O2 + 4 H2O decomposition • 2 Al + Fe2O3 → Al2O3 + 2 Fe replacement • MgCl2 + K2S → MgS + 2 KCl replacement • P4O10 + 6H2O → 4 H3PO4

  19. Classifying Chemical Reactions • PracticeClassify each of the following reactions as synthesis, decomposition, or replacement. • 2 NH4NO3 → 2 N2 + O2 + 4 H2O decomposition • 2 Al + Fe2O3 → Al2O3 + 2 Fe replacement • MgCl2 + K2S → MgS + 2 KCl replacement • P4O10 + 6H2O → 4 H3PO4 synthesis

  20. 8.3 Energy and Chemical Change Products have a higher energy level than the reactants in an endothermic reaction. A False B True

  21. 8.3 Energy and Chemical Change ____ bonds ____ energy. A Breaking; releases B Breaking; requires C Forming; requires D Ionic; release

  22. 8.3 Energy and Chemical Change The law of ____ states that energy is neither created nor destroyed in a chemical reaction. A conservation of mass B definite proportions C conservation of matter D conservation of energy

  23. Which does NOT describe an exothermic reaction? AThere is a net release of energy. BThe reactants have a higher energy than the products . CThe reactants are lower in energy than the products. D The products are less stable than the reactants.

  24. SCI 5.c Energy is ____ in exothermic reactions. A absorbed B created C released D stored

  25. Vocab – Energy and Chemical ChangeText p.358-363. For #5-8, use your notes. • chemical bond • law of conservation of energy • exothermic process • endothermic process • activation energy • synthesis reaction • decomposition reaction • replacement reaction

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