Difference between revisions of "Bond Energy"

Revision as of 12:04, 28 October 2019

Key Stage 4 Higher

Meaning

Bond Energy is the energy needed to break a chemical bond between two atoms.

About Bond Energy

When chemical bonds are formed energy is released to the surroundings increasing the temperature. An exothermic process]].

To break chemical bonds energy is needed to separate the atoms, decreasing the temperature of the surroundings. An endothermic process]].

Examples

Some common bond energies are given in the table below.

Bond	Energy in kJ/mol
H-H	436
O=O	498
N≡N	941
C-C	347
C=C	614
C≡C	839
C-H	413
O-H	464
C=O	799
Cl-Cl	243
H-Cl	432
N-H	391

These can be used to calculate the energy released per mole in a chemical reaction.

Example 1


In the reaction between Methane and Oxygen the chemical bonds in the reactants must be broken first before the bonds in the products are formed.

There are 4 C-H bonds and 2 O=O bonds.

4 x 413 + 2 x 498 = 2648kJ

Therefore 2648kJ/mol are needed to break the bonds in the reactants.

There are 2 C=O bonds and 4 O-H bonds.

2 x 799 + 4 x 464 = 3454kJ

Therefore 3454kJ/mol is released when the bonds in the products form.

Once the reaction is complete 806kJ will be released.

Example 2


In the reaction between Hydrogen and Nitrogen the chemical bonds in the reactants must be broken first before the bonds in the products are formed.

There are 3 H-H bonds and 1 N≡N bonds.

3 x 436 + 1 x 941 = 2249kJ

Therefore 2249kJ/mol are needed to break the bonds in the reactants.

There are 6 N-H bonds.

6 x 391 = 2346kJ

Therefore 2346kJ/mol is released when the bonds in the products form.

Once the reaction is complete 97kJ will be released.

References

AQA

Bond energies, page 63, GCSE Chemistry; The Revision Guide, CGP, AQA

Bond energies, pages 133-5, GCSE Chemistry, Hodder, AQA

Bond energies, pages 158, 159, GCSE Combined Science Trilogy; Chemistry, CGP, AQA

Bond energies, pages 183, 184, GCSE Chemistry, CGP, AQA

Bond energies, pages 235-7, GCSE Combined Science Trilogy 1, Hodder, AQA

Bond energy, pages 117-119, GCSE Chemistry; Third Edition, Oxford University Press, AQA

@@ Line 96: / Line 96: @@
 Once the [[Chemical Reaction|reaction]] is complete 97kJ will be released.
+===References===
+====AQA====
+:[https://www.amazon.co.uk/gp/product/1782945571/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782945571&linkCode=as2&tag=nrjc-21&linkId=9e29fad914244909903e5e93f8a01d62 ''Bond energies, page 63, GCSE Chemistry; The Revision Guide, CGP, AQA '']
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+:[https://www.amazon.co.uk/gp/product/178294639X/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=178294639X&linkCode=as2&tag=nrjc-21&linkId=51599bb45a2bfaf7c1b6a978b2ca2616 ''Bond energies, pages 158, 159, GCSE Combined Science Trilogy; Chemistry, CGP, AQA '']
+:[https://www.amazon.co.uk/gp/product/1782945962/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782945962&linkCode=as2&tag=nrjc-21&linkId=476bb5c8d1dfb5c08ac81b6d4d1c98d8 ''Bond energies, pages 183, 184, GCSE Chemistry, CGP, AQA '']
+:[https://www.amazon.co.uk/gp/product/1471851354/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1471851354&linkCode=as2&tag=nrjc-21&linkId=9012a0d354024419214fb3ad5ac44ba0 ''Bond energies, pages 235-7, GCSE Combined Science Trilogy 1, Hodder, AQA '']
+:[https://www.amazon.co.uk/gp/product/0198359381/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=0198359381&linkCode=as2&tag=nrjc-21&linkId=47c8d1ae58d8b3a5e2094cd447154558 ''Bond energy, pages 117-119, GCSE Chemistry; Third Edition, Oxford University Press, AQA '']