1. ENTHALPY

2. OBJECTIVES  Exothermic changes cause heat to be released to the surroundings  Endothermic changes cause absorption of heat from the surroundings.  A potential energy diagram can be used to show the energy pathway for a reaction.  The enthalpy change is the energy difference between products and reactants.

3. Enthalpy Diagrams Exothermic reactions energy course of reaction

4. Energy Level Diagrams Exothermic reactions energy course of reaction reactants

5. Energy Level Diagrams Exothermic reactions energy course of reaction reactants products

6. Energy Level Diagrams Exothermic reactions energy course of reaction reactants products energy given out ∆H is negative

7. Energy Level Diagrams Endothermic reactions energy course of reaction

8. Energy Level Diagrams Endothermic reactions energy course of reaction reactants

9. Energy Level Diagrams Endothermic reactions energy course of reaction reactants products

10. Energy Level Diagrams Endothermic reactions energy course of reaction energy taken in ∆H is positive reactants products

11. Summary Table Exothermic reactions Endothermic reactions

12. Summary Table Exothermic reactions Endothermic reactions Energy is given out to the surroundings Energy is taken in from the surroundings

13. 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

14. 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

15. ∆H 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

16. C H H HH O O O O

17. C HHHHOOOO Energy absorbed to break bonds

18. C HHHHOOOO

19. C HHHHOOOO Energy released when new bonds are made

20. Overall energy change = Energy released on making new bonds - Energy taken in to break old bonds

21. Energy Level Diagrams Exothermic reactions energy course of reaction methane + oxygen carbon dioxide + water

22. Reaction mixture Test tube

23. Heat given out to surroundings EXOTHERMIC

24. Heat taken in from surroundings ENDOTHERMIC

25. TASK  Draw energy level diagrams for the following reactions: 1.Photosynthesis 2.Calcium with sulphuric acid 3.Dissolving ammonium nitrate