Chemistry Chapter 13: Nitrogen

CHEMISTRY KEYWORDS:

Eutrophication: Environmental problem caused by fertilisers leached from fields into rivers and lakes.

Hydrocarbon: Organic compound made up of hydrogen and carbon only.

PAN: Organic pollutant made by reactions with nitrogen oxides, in sunlight, causing photochemical smog. Peroxyacetyl nitrate CH₃CO₃NO₂

Photochemical Reactions: Reactions started by energy from ultraviolet light.

CHEMISTRY IMPORTANT NOTES:

Nitrogen is in Group 15 of the Periodic Table. It is a non-metallic element that makes up about 78% of the Earth’s atmosphere.

The triple covalent bond is very strong. Its bond energy is almost 1000 kJ/mol. This bond is difficult to break so nitrogen gas will only react under extreme conditions.

Step 1: Lightning provided of high activation energy needed for the oxidation of the unreactive nitrogen gas to form nitrogen (II) oxide. N₂(g) + O₂(g) -> 2NO(g)

Step 2: Nitrogen (II) oxide formed is then further oxidised by oxygen in the air to give nitrogen (IV) oxide. 2NO(g) + O₂(g) -> 2NO₂(g)

Step 3: Nitrogen (IV) oxide dissolves in water droplets in the air and reacts with more oxygen, to form a dilute solution of nitric acid. The dilute acid falls to the Earth in rain. 2NO₂(g) + H₂O(l) + 0.5O₂ -> 2HNO₃(aq)

N₂(g) + 3H₂(g) -> 2NH₃(g)

Ammonia is a weak base, while ammonium ion is an acid.

Nitrogen oxides pollute our atmosphere. They cause acid rain and photochemical smog.

 

SUMMARY:

Nitrogen is a very unreactive gas because of the high bond energy of the triple bond.

Ammonia is a very common compound of nitrogen. Its molecules have a triangular pyramidal shape.

An ammonia molecule can act as a base, accepting an H⁺ ion to form an ammonium ion, NH₄⁺.

Ammonia gas is given off from ammonium salts by heating them with a base.

Nitrogen oxides are formed naturally during lightning strikes when nitrogen gas is oxidised. These gaseous nitrogen oxides are also formed in internal combustion engines and become pollutants in the atmosphere, contributing to acid rain.

Sulfur dioxide gas is the main cause of acid rain. In the atmosphere, the oxidation of sulfur dioxide to sulfur trioxide is catalysed by oxides of nitrogen.

PAN, peroxyacetyl nitrate, is a pollutant found in photochemical smog. It is formed by reactions between oxides of nitrogen and unburnt hydrocarbons and other VOCs (volatile organic compounds).