1. Agenda: April 12th  Warm-up: A change requires energy.  Chemical reactions and energy  Endothermic or exothermic  How energy is represented in chemical reactions  Practice: Predicting products  Mixed Practice

3. Representing the energy changes in reactions Thermo-chemistry

5. Representing energy in chemical reactions 1. Measurement of energy: joules Joules/gram or joules/mole 2. Energy shown as a reactant or product Endothermic: Exothermic: 3. Change in energy: ∆H (heat of reaction) Positive + ∆ Negative -∆ 4. Diagrams of the energy

6. ENERGY IN REACTIONS Exothermic reactions Energy is given out The products have less energy than the reactants Exothermic reactions are common. Combustion and neutralization (a special type of double replacement reactions) are exothermic

7. ENERGY LEVEL DIAGRAMS Exothermic reactions energy

8. ENERGY LEVEL DIAGRAMS Exothermic reactions energy course of reaction

9. ENERGY LEVEL DIAGRAMS Exothermic reactions energy course of reaction reactants

10. ENERGY LEVEL DIAGRAMS Exothermic reactions energy course of reaction reactants products

11. ENERGY LEVEL DIAGRAMS Exothermic reactions energy course of reaction reactants products energy given out ∆H is negative

12. ENERGY LEVEL DIAGRAMS Endothermic reactions Energy is taken in The products have more energy than the reactants The energy is taken in from the surroundings

13. ENERGY LEVEL DIAGRAMS Endothermic reactions energy

14. ENERGY LEVEL DIAGRAMS Endothermic reactions energy course of reaction

15. ENERGY LEVEL DIAGRAMS Endothermic reactions energy course of reaction reactants

16. ENERGY LEVEL DIAGRAMS Endothermic reactions energy course of reaction reactants products

17. ENERGY LEVEL DIAGRAMS Endothermic reactions energy course of reaction energy taken in ∆H is positive reactants products

18. SUMMARY TABLE Exothermic reactions Endothermic reactions

19. SUMMARY TABLE Exothermic reactions Endothermic reactions Energy is given out to the surroundings Energy is taken in from the surroundings

20. SUMMARY TABLE Exothermic reactions Endothermic reactions Energy is given out to the surroundings Energy is taken in from the surroundings ∆H is negative∆H is positive

21. SUMMARY TABLE Exothermic reactions Endothermic reactions Energy is given out to the surroundings Energy is taken in from the surroundings ∆H is negative∆H is positive Products have less energy than reactants Products have more energy than reactants

22. ∆H = ENTHALPY = CHANGE IN ENERGY How much energy is given out or taken in? Energy is needed to break chemical bonds Energy is given out when bonds are made ∆H is the difference between the energy needed to break the bonds in the reactants, and the energy given out when new bonds are made in the products

23. WORKING OUT ∆H Summary The energy values have units of kJ/mole ∆H is difference between energy in – energy out Energy goes in to break bonds Energy goes out when bonds are made

24. Practice: Reactions  Determine types of reactions  Determine if the reaction is endothermic or exothermic