1. Energy Levels A Creative Chemistry PowerPoint Presentation By Nigel Saunders Copyright © 2003 Nigel Saunders, all rights reserved Permission is granted for personal and educational use only. Commercial copying, hiring, lending is prohibited.

2. Energy Levels Exothermic reactions Energy is given out The products have less energy than the reactants Combustion and neutralisation are exothermic

3. Energy Level Diagrams Exothermic reactions energy

4. Energy Level Diagrams Exothermic reactions energy course of reaction

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

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

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

8. 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

9. Energy Level Diagrams Endothermic reactions energy

10. Energy Level Diagrams Endothermic reactions energy course of reaction

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

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

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

14. Summary Table Exothermic reactions Endothermic reactions

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

16. 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

17. 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

18. ∆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

19. Bond energies The energy needed to break a chemical bond Different chemical bonds have different bond energies Chemical bondBond energy, kJ/mole H―H436 O=O498 O―H464

20. Working out ∆H Draw an energy level diagram with all the reactants and products on it energy course of reaction 2H 2 + O 2 2H 2 O

21. Working out ∆H Show all the bonds in the reactants energy course of reaction 2H 2 O H―H O=O+

22. Working out ∆H Show all the bonds in the products energy course of reaction H―H O=O+ HH O HH O

23. Working out ∆H Show the bond energies for all the bonds energy course of reaction 436 O=O+ HH O HH O

24. Working out ∆H Show the bond energies for all the bonds energy course of reaction 436 498+ HH O HH O

25. Working out ∆H Show the bond energies for all the bonds energy course of reaction 436 498+ HH O 464 +

26. Working out ∆H Show the bond energies for all the bonds energy course of reaction 436 498+ 464 + +

27. Working out ∆H Add the reactants’ bond energies together energy course of reaction 464 + + 1370

28. Working out ∆H Add the products’ bond energies together energy course of reaction 1370 1856

29. Working out ∆H ∆H = energy in ― energy out energy course of reaction 1370 1856 1370 1856 ―

30. Working out ∆H ∆H = energy in ― energy out energy course of reaction 1370 1856 1370 1856 -486 ―

31. Working out ∆H ∆H = energy in ― energy out energy course of reaction 1370 1856 ∆H = -486

32. Working out ∆H Summary The energy values have units of kJ/mole In the exam, you will be given the energy values and all the bonds to make or break ∆H is energy in – energy out Energy goes in to break bonds Energy goes out when bonds are made