Bond Energy 5.3
Every reaction has an associated quantity of energy
Every reaction has an associated quantity of energy True for both chemical or physical changes
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
For all elements except the noble gases…….
For all elements except the noble gases……. Isolated atoms are not stable
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
Consider the H2 example
Consider the H2 example The diatomic molecule is most stable
Consider the H2 example The diatomic molecule is most stable As the lone atoms approach, interaction starts e + + e
Consider the H2 example The protons are attracted to the electrons e e + + e
Consider the H2 example The protons are attracted to the electrons At some distance e-repel/ protons repel e + + e
Consider the H2 example The attractive and repulsion forces balance e + + e
Consider the H2 example The attractive and repulsion forces balance This is when the 2 atoms are at a minimum potential energy e + + e
Energy Internuclear Distance
Energy Internuclear Distance
Energy Internuclear Distance
Energy Internuclear Distance
Energy Bond Energy Internuclear Distance
Continuing with the H2 Example
Continuing with the H2 Example Bond energy is associated with bond length.
Bond energy is associated with bond length. H-H
Bond energy is associated with bond length. H-H 75 picometer
H-H Bond energy is associated with bond length. 75 picometer 436 kj/mol
H-H Bond energy is associated with bond length. 75 picometer 436 kj/mol Recall the inverse relationship between bond length and bond energy
H-H Bond energy is associated with bond length. 75 picometer 436 kj/mol Recall the inverse relationship between bond length and bond energy For H2 ….Fairly strong bond—energy to break is fairly high
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
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
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
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
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
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- 11786KJ= -1077KJ C-C 347 kJ/mol 32