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 reactants
course of reaction

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

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

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 reactants
course of reaction

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

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

14. Endothermic reactions
Summary Table
Exothermic reactions
Endothermic reactions

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

16. Endothermic reactions
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. Endothermic reactions
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 bond
Bond energy, kJ/mole
H―H
436
O=O
498
O―H
464

20. Working out ∆H
Draw an energy level diagram with all the reactants and products on it
energy
2H2 + O2
2H2O
course of reaction

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

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

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

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

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

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

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

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

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

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

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

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
Energy goes in to break bonds
Energy goes out when bonds are made
∆H is energy in – energy out