1. Bond Energy 5.3

2. Every reaction has an associated quantity of energy

3. Every reaction has an associated quantity of energy
True for both chemical or physical changes

4. Bond Energy and Lattice Energy
Every reaction has an associated quantity of energy
True for both chemical or physical changes
But chemical bonds form for the purpose of lowering the potential energy associated with an atom

5. For all elements except the noble gases…….

6. For all elements except the noble gases…….
Isolated atoms are not stable

7. For all elements except the noble gases…….
Isolated atoms are not stable
Attractive forces that occur when bonding to another atoms produces a more stable arrangement than single atoms

8. Consider the H2 example

9. Consider the H2 example
The diatomic molecule is most stable

10. Consider the H2 example The diatomic molecule is most stable
As the lone atoms approach, interaction starts e + + e

11. Consider the H2 example The protons are attracted to the electrons e e+ + e

12. Consider the H2 example The protons are attracted to the electrons
At some distance e-repel/ protons repel e + + e

13. Consider the H2 example The attractive and repulsion forces balance e+ + e

14. Consider the H2 example The attractive and repulsion forces balance
This is when the 2 atoms are at a minimum potential energy e + + e

15. Energy
Internuclear Distance

16. Energy
Internuclear Distance

17. Energy
Internuclear Distance

18. Energy
Internuclear Distance

19. Energy
Bond Energy
Internuclear Distance

20. Continuing with the H2 Example

21. Continuing with the H2 Example
Bond energy is associated with bond length.

22. Bond energy is associated with bond length.
H-H

23. Bond energy is associated with bond length.
H-H
75 picometer

24. H-H Bond energy is associated with bond length.
75 picometer kj/mol

25. H-H Bond energy is associated with bond length.
75 picometer kj/mol
Recall the inverse relationship between bond length and bond energy

26. H-H Bond energy is associated with bond length.
75 picometer kj/mol
Recall the inverse relationship between bond length and bond energy
For H2 ….Fairly strong bond—energy to break is fairly high

27. Consider other bond energies
Element to element bond
Bond energy, kJ/mol
F-F
159
H-F
569
O-H
459
N-N
180
C-C
346
C=C
612

28. Consider other bond energies
This is the energy released when the bond forms
(-159 for F-F)
……..or
The energy required to break the bond
(+159 for F-F)
Element to element bond
Bond energy, kJ/mol
F-F
159
H-F
569
O-H
459
N-N
180
C-C
346
C=C
612

29. Find the energy for this reaction
2 CH2 = CHCH3 +
2NH3
3 O2 +
2 CH2 = CHC º N +
6 H2O
C-H 413 kJ/mol
O-H 467 kJ/mol
C=C 614kJ/mol
O=O 495 kJ/mol
N-H 391 kJ/mol
CºN 891 kJ/mol
C-C 347 kJ/mol

30. Find the energy for this reaction
2 CH2 = CHCH3 +
2NH3 O2 +
12x C-H 413 kJ/mol
O-H 467 kJ/mol
2x C=C 614kJ/mol
3x O=O 495 kJ/mol
6x N-H 391 kJ/mol
CºN 891 kJ/mol
Total bond energy Reactants=10709KJ
2x C-C 347 kJ/mol 30

31. Find the energy for this reaction
2 CH2 = CHC º N +
6 H2O
6x C-H 413 kJ/mol
12 O-H 467 kJ/mol
2x C=C 614kJ/mol
0x O=O 495 kJ/mol
0x N-H 391 kJ/mol
2x CºN 891 kJ/mol
Total bond energy for the products= 11786KJ
2x C-C 347 kJ/mol 31

32. Find the energy for this reaction
2 CH2 = CHCH3 +
2NH3
3 O2 +
2 CH2 = CHC º N +
6 H2O
C-H 413 kJ/mol
O-H 467 kJ/mol
C=C 614kJ/mol
O=O 495 kJ/mol
N-H 391 kJ/mol
CºN 891 kJ/mol
Enthalpy change= 10709KJ KJ= -1077KJ
C-C 347 kJ/mol 32