Notes - Energy & Chemical Change

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