# Air Quality - Chemical Reactions and Pollutants

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When there is a chemical reaction, air pollutants are produced. You can understand how these pollutants are formed by looking at what happens to atoms during these chemical reactions.

Formulae

The chemical formula of a compound tells you how many atoms of each element the molecule contains. The small (subscript) number after a symbol tells you how many atoms of that particular element are in the molecule. If there is only one atom of an element in a molecule, we do not write the number 1 after the symbol. For example, the water molecule H20 has two hydrogen and one oxygen atom.

Rearrangement of Atoms

In a chemical reaction, the substances that react together are called the reactants, while the substances that are formed are called the products. Reactants --> products. The products have different properties from the reactants. As a chemical reaction takes place, atoms in the reactants are rearranged to make the products. No atoms are added or taken away. This is called the conservation of atoms. As the atoms are conserved and all atoms have mass, the mass of the reactants will be the same as the mass of the products. This is known as conservation of mass. Oxidation reactions is when a reaction is joining with oxygen. When oxygen is removed from a chemical the reaction is known as a reduction reaction.

Burning Fuels

Burning fuels releases harmful pollutants into the air. Pollutants can kill plants, harm our lungs, cause acid rain and are thought to contribute to global warming. A combustion reaction is when a chemical reacts with oxygen and releases energy. We burn fuels to produce energy. When these fuels burn, the atoms in the fuels combine with oxygen from the air to make new molecules. Coal is made mainly of carbon. This burns to produce carbon dioxide. Petrol, diesel fuel and fuel oil are hydrocarbons. Their molecules are made of carbon and hydrogen atoms. When these fuels burn, the carbon and hydrogen atoms combine with oxygen atoms to produce carbon dioxide and water vapour.

Making Pollutants

Fuels are burned in the vehicles we use for transport, and in power stations to make electricity. When fuels are burned, pollutants are formed and released into the air. The combustion of fuels increases the concentration of carbon dioxide in the air. This is thought to cause global warming.

Properties

The products have different properties from the reactants. Many fuels contain small amounts of sulfur compounds. When these fuels are burned sulfur dioxide is released into the air. Sulfur dioxide causes acid rain that can damage buildings and kill plants.

Incomplete Combustion

If there is not enough oxygen present to burn the fuels completely, incomplete combustion takes place. Carbon monoxide, a very poisonous gas, is formed. Incomplete combustion also releases very small particles of carbon into the air. This particulate carbon makes buildings dirty and can cause breathing difficulties.

Nitrogen Oxides

In the high temperatures of vehicle engines, nitrogen and oxygen react to form nitrogen