FERTILISERS

Why? How? How long? Advantages? Disadvantages?

Why do we use fertilisers and how long have they been around?

Fertilisers are used in farming and the production of plants for sale to make them grow faster, larger and be overall more healthy. They were first used on a large scale during the industrial Green Revolution in the early 20th Century.

How do we make them?

Fertilisers are made by reacting an acid and an alkali together. Ammonium nitrate is made using nitric acid and ammonia; ammonium phosphate is made using phosphoric acid and ammonia; ammonium sulfate is made using sulfuric acid and ammonia and potassium nitrate is made using nitric acid and potassium hydroxide.

Advantages and Disadvantages

Fertilisers increase crop yields and can make crops grow faster and bigger. This means that a farmer can earn more money when he sells them. However, they cause damage to the environment through eutrophication when rainwater washed them into rivers and lakes.

What is the Haber Process?

The Haber Process is an important industrial process that produces ammonia, a substance that is needed for making fertilisers. Nitrogen and Hydrogen are needed to make ammonia. The nitrogen is easily extracted from the air and hydrogen is obtained from natural gas. The reaction is reversible so not all of the nitrogen and hydrogen will react. The reaction reaches a dynamic equilibrium.


The industrial manufacture of ammonia uses the following conditions:

Pressure: 200 atmospheres

Temperature: 450 degrees C

Catalyst: Iron


The pressure is set as high as possible to give the best percentage yield without making the plant too costly to build and run.


The reaction is exothermic so the increasing of temperatures will reverse the reaction and cause ammonia to break down into H2 and N2. Lower temperatures mean a greater yield of ammonia. Lowering the temperatures lower the rate of reaction so the temperature is raised to get a faster reaction.


The ammonia is formed as a gas but the condenser cools it, liquifying it and then it is removed.


The iron is only a catalyst. It makes the reaction go faster but it doesn't affect the percentage yield.