Importance, Composition and Properties of Air

Air is the homogeneous mixture of gases that make up the earth's atmosphere. Thanks to him the biological processes (like breathing) and biogeochemical cycles (like the water cycle). It is the environment in which weather conditions occur and is made up of a variety of elements and chemical compounds.

Percentage composition of air

The air contains the following elements and chemical compounds, naturally balanced to support the processes of the planet:

• Nitrogen (N₂): 78%
• Oxygen (O₂): 21%
• Argon (Ar): 0.9%
• Carbon dioxide (CO₂): 0.03%
• The other 0.07% is made up of varying proportions of water vapor (H₂O), hydrogen (H₂), ozone (O₃), methane (CH₄), carbon monoxide (CO), helium (He), neon (Ne), krypton (Kr), and xenon (Xe).

Importance of air oxygen

Oxygen is a very reactive chemical element capable of getting involved with a wide variety of elements, such as metals, non-metals and metalloids. What's more, it is essential for the respiration of all living beings. Its presence in the air is, therefore, what preserves life on the planet.

Oxygen is the oxidizer by excellence. That is, it is the substance that preserves the combustion reactions. When a substance that contains carbon enters a combustion reaction, it will combine with oxygen to release its carbon atoms as carbon dioxide (CO₂) or carbon monoxide (CO), depending on the quality of the reaction.

Importance of nitrogen in the air

78% nitrogen (N₂) is vital, because it is the element in charge of dampen oxygen reactivity. 21% oxygen (O₂) is enough to make all the combustible matter on the planet ignite. However, there is the presence of nitrogen gas (N₂), which is inert at atmospheric temperatures.

If the percentage of oxygen (O₂) exceeds 21%, we would be lost: all the organic matter on the planet would spontaneously burn, accompanied by solar radiation. The same effect would occur if the percentage of nitrogen (N₂) will drop from 78%. It is therefore essential to maintain the balance between these two components of the air, and to prevent excess air pollution.

Oxygen reactions

The oxygen in the air (O₂) is a chemical reagent available to many substances, so that they begin to transform into others, which will have different physical and chemical properties. Each transformation is going to be described with a chemical equation. Among the reactions in which oxygen participates are:

• Combustion reactions
• Oxidation reactions
• Synthesis reactions

In the combustion reactions, oxygen is going to join the carbon atoms of a combustible substance, to give off a large amount of heat and combustion gases: carbon dioxide (CO₂) or carbon monoxide (CO). In addition to these products, water vapor is generated.

In the oxidation reactions, the oxygen is going to bind to the atoms of the metallic elements, in a corrosion phenomenon called oxidation. Metal oxides will be formed as products.

In the synthesis reactions, oxygen is going to combine with non-metallic elements to form their respective oxides, also called anhydrides. These are generally gases, such as nitrogen oxides (NOx's), sulfur oxides (SOx's), and they are air pollutants.

Examples of oxygen reactions

1.- The combustion of methane gas (CH₄):

CH₄ + (3/2) O₂ -> CO₂ + 2H₂OR

2.- The combustion of ethane gas (C₂H₆):

C₂H₆ + (7/2) O₂ -> 2CO₂ + 3H₂OR

3.- The combustion of propane gas (C₃H₈):

C₃H₈ + 5O₂ -> 3CO₂ + 4H₂OR

4.- The combustion of butane gas (C₄H₁₀):

C₄H₁₀ + (13/2) O₂ -> 4CO₂ + 5H₂OR

5.- The oxidation of the metal iron (Fe) to form ferric oxide:

2Fe + (3/2) O₂ -> Faith₂OR₃

6.- The oxidation of iron metal (Fe) to form ferrous oxide:

Fe + (1/2) O₂ -> FeO

7.- The oxidation of the metal sodium (Na) to form sodium oxide (Na₂OR):

2Na + (1/2) O₂ -> Na₂OR

8.- The synthesis of nitric oxide (NO):

N₂ + O₂ + heat -> 2NO

9.- The synthesis of sulfur dioxide (SO₂):

S + O₂ + heat -> SO₂

10.- The synthesis of sulfur trioxide (SO₃):

S + (3/2) O₂ + heat -> SO₃

Air pollutants

Despite the planet's efforts to balance the concentrations of atmospheric components, human activities generate a large amount of intrusive substances: pollutants. Pollutants are chemical species that alter the properties of the air and its functions to support life. Among them are:

• Carbon monoxide (CO), the main source of which is incomplete combustion in internal combustion engines.
• Sulfur dioxide (SO₂), whose main source is sulfuric acid producing plants.
• Suspended particles, which come from combustion in engines. Particles smaller than 10 microns (PM10) are included, which can reach the respiratory system of living beings and cause diseases.
• Lead (Pb), whose main source is the furnaces of the smelting plants.
• Long-chain hydrocarbons, which come from oil, and are released during oil burning.

Follow with:

• Characteristics of oxygen