BOND ENERGY CALCULATIONS 2
Bond
N-N
C-C
C-O
N-H
C-H
H-H
Bond energy (kJ/mol)
158
348
360
388
412
436
Bond
O-H
O=O
C=C
C=O
N≡N
Bond energy (kJ/mol)
463
498
612
743
944
For each of the following reactions, use the bond energy data to:
a)
calculate the energy required to break the bonds in the reactants
b)
calculate the energy released when the bonds in products are made
c)
calculate the energy change for the reaction
d)
state whether the reaction is exothermic or endothermic
1
H
2 H
vi)
Break
2 H-H
O=O
Total
2
+
H
O
2 H
Make
4 O-H
Total
2(436)
498
1370
H
H
H iii) C
C
Break
C=C
4 C-H
3 O=O
Total
H
+
3O
O
4(463)
1852
Energy change = break – make
= 1370 – 1852
= –482 kJ/mol
2 O
O
Make
4 C=O
4 O-H
Total
612
4(412)
3(498)
3754
H
4(743)
4(463)
4824
C
O
+
x)
H
Break
N-N
4 N-H
O=O
Total
O
Exothermic
More energy released making bonds than
needed to break bonds
H
Exothermic
More energy released making bonds than
needed to break bonds
H
+
N
2 H
Energy change = break – make
= 3754 – 4824
= –1070 kJ/mol
H
N
3
O
O
O
N
N
+
2 H
O
H
158
4(388)
498
2208
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Make
N≡N
4 O-H
Total
944
4(463)
2796
Energy change = break – make
= 2208 – 2796
= –588 kJ/mol
22-May-2018
Exothermic
More energy released making bonds than
needed to break bonds
Chemsheets GCSE 1155
H
H
Hvii) C
C
H
H
4
Break
C-C
5 C-H
C-O
O-H
Total
5
H
O
H
Make
C=C
4 C-H
2 O-H
Total
348
5(412)
360
463
3231
H
H
H
iv) C
C
C
H
+
H
H
H
C
C
H
H
612
4(412)
2(463)
3186
H
+
Make
2 C-C
8 C-H
Total
612
348
6(412)
436
3868
H
Area
2(348)
4(412)
3992
H
H
H
C
C
C
H
H
H
H
Done with care and thoroughness
Adds up make/break well
Suitable working
Finds energy change
Counts bonds well
States if endo/exothermic
Endothermic
Less energy released making bonds than
needed to break bonds
H
Energy change = break – make
= 3868 – 3992
= –124 kJ/mol
Strength To develop Area
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O
Energy change = break – make
= 3231 – 3186
= –+45 kJ/mol
H
Break
C=C
C-C
6 C-H
H-H
Total
H
Exothermic
More energy released making bonds than
needed to break bonds
Strength To develop Area
Strength To develop
Can explain if endo/exothermic
22-May-2018
Chemsheets GCSE 1155