University Federico II
of Naples, Italy
European Chemistry
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Combustion of methane

Methane is a natural gas that is extracted and used as a fuel. It is the major component of gas used in kitchens and heaters in many countries.

A methane molecule is composed of one Carbon atom and 4 Hydrogen atoms. Its formula is CH4. The four hydrogen atoms are bonded to the central carbon atom and are directed in four non-coplanar directions. The molecule is three-dimensional and its shape is called tetrahedral.

When Methane burns, C-H bonds are broken. Both C and H atoms form new bonds with Oxygen, yielding Carbon dioxide CO2 and Water H2O. Oxygen is found in air as O2 molecules:

CH4

+

O2

=

CO2

+

H2O

   

It is apparent, however, that one Oxygen molecule is not sufficient to burn one Methane molecule. Methane contains 5 atoms (1 C and 4 H).

The C atom needs 2 O atoms to form one CO2 molecule. A couple of H atoms needs one O atom to form one H2O molecule, and there are two such couples. Summing up, the methane molecule requires 4 O atoms, that are found in 2 oxygen O2 molecules.

From one methane molecule one carbon dioxide molecule is formed, containing the C atom, and two water molecules, containing the 4 hydrogen atoms. Two oxygen molecules are consumed to provide the 4 oxygen atoms.

The full balance is:

CH4

+

2 O2

=

CO2

+

2 H2O






This is the balanced reaction. The numbers in front of the chemical formulas are the reaction coefficients. They indicate the ratios between numbers of molecules: for one methane molecule, two oxygen molecules must react, producing one molecule of carbon dioxide and two water molecules. With the proper coefficients, the reaction equation shows that the same number of atoms in the reagents is found in the products: