Name/s: ________________________
BOND ENERGY
Class: Y10 - _____
Date: _______________
CALCULATIONS
1
BOND ENERGY CALCULATIONS
Bond
Br-Br
Cl-Cl
C-Br
C-C
C-O
C-H
H-Cl
Bond energy (kJ/mol)
193
242
276
348
360
412
431
Bond
S=O
H-H
O-H
O=O
C=C
C=O
H-Br
Bond energy (kJ/mol)
435
436
463
498
612
743
366
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
e)
explain why the reaction is exothermic or endothermic in terms of bond breaking and making
1
H
H
Break
H-H
Br-Br
Total
2
H
H
Br
H
H
C
C
Make
2 H-Br
Total
H
+
Br
Make
C-C
4 C-H
2 C-Br
Total
612
4(412)
193
2453
H
+
2
Br
436
193
629
Break
C=C
4 C-H
Br-Br
Total
3
+
Cl
H
Br
Energy change = break – make
= 629 – 732
= –103 kJ/mol
2(366)
732
Br
H
H
C
C
Br
Br
H
Energy change = break – make
= 2453 – 2548
= –95 kJ/mol
348
4(412)
2(276)
2548
2
Cl
H
H
Exothermic
More energy released making bonds than
needed to break bonds
Exothermic
More energy released making bonds than
needed to break bonds
Cl
ii)
Break
H-H
Cl-Cl
Total
436
242
678
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Make
2 H-Cl
Total
2(431)
862
Energy change = break – make
= 678 – 862
= –184 kJ/mol
20-February-2017
Exothermic
More energy released making bonds than
needed to break bonds
Chemsheets GCSE 1154
O
4
2
O
S
+
O
O
O
S
2
O
O
Break
4 S=O
O=O
Total
Make
6 S=O
Total
4(435)
498
2238
H
H
H
Hiii) C
C
C
H
H
H
Energy change = break – make
= 2238 – 2610
= –372 kJ/mol
6(435)
2610
Exothermic
More energy released making bonds than
needed to break bonds
O
5
Break
2 C-C
8 C-H
5 O=O
Total
6
H
+
H
Make
6 C=O
8 O-H
Total
2(348)
8(412)
5(498)
6482
H
H
H
C
C
C
5 O
H
+
Br
3
O
O
7
H
H
H
O
C
viii)
C
C
H
H
Break
2 C-C
2 C-O
C=O
8 C-H
2 O-H
Total
Make
2 C-C
2 C-Br
6 C-H
Total
348
612
6(412)
193
3625
6(743)
8(463)
8162
Br
H
H
2(348)
2(360)
743
8(412)
2(463)
6381
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+
H
C
O
H
Make
2 C-C
2 C-O
C=O
8 C-H
2 O-H
Total
2(348)
2(360)
743
8(412)
2(463)
6381
+
4
H
H
H
H
C
C
C
H
Br
Br
H
H
H
H
O
C
C
C
H
H
H
Exothermic
More energy released making bonds than
needed to break bonds
H
O
Energy change = break – make
= 6381 – 6381
= 0 kJ/mol
20-February-2017
H
Exothermic
More energy released making bonds than
needed to break bonds
Energy change = break – make
= 3625 – 3720
= –95 kJ/mol
2(348)
2(276)
6(412)
3720
H
O
O
Energy change = break – make
= 6482 – 8162
= –1680 kJ/mol
H
Break
C-C
C=C
6 C-H
Br-Br
Total
C
C
H
H
+
H
O
H
Neither exothermic nor endothermic
Same amount of energy released making
bonds as is needed to break bonds
Chemsheets GCSE 1154