Ammonia and the Haber process

Plants need nitrogen in order to make protein and then grow. Most plants cannot use nitrogen in the form of N2 (How it is found in the

atmosphere). Plants need their supply of nitrogen in the form of the soluble compounds, Nitrates.

Nitrates are artificially given to plants in fertilisers. To make a fertiliser you have to start with ammonia (NH3). Ammonia is a compound of Nitrogen and Hydrogen. Ammonia is made using the Haber process. The Haber process was designed by the

chemist Fritz Haber.

Nitrogen + Hydrogen AmmoniaN2 + 3H2 2NH3

= a reversible reaction. Conditions needed to make ammonia ...

200-300 atmospheres pressure, 400-500°C Iron Catalyst,

The atom economy of this reaction is 100%. This is because only one product is made.

Although the atom economy is 100%, the percentage yield is approximately 15% because the Ammonia can (and does) change back into Hydrogen and Nitrogen. The unreacted Nitrogen and Hydrogen are recycled.

As the temperature increases the yield of ammonia decreases, As the pressure increases the yield of ammonia increases, Ammonia is made at 400-500°C because at lower temperatures the rate of reaction

is too slow.

100 400300 500200

600°C

450°C

350°C

550°C

Lower pressures are used because high pressures (such as 500 atmospheres) are hard to obtain, expensive and dangerous.

Fertilisers

Ammonia is an alkali. Most plants prefer neutral soils, so ammonia is neutralised with acids when it is

turned into fertilisers. Therefore making fertilisers is a neutralisation reaction. Not all fertilisers are made using ammonia (E.g. Potassium Nitrate).

Ammonia Solution + Sulphuric Acid ---> Ammonium Sulphate + WaterAmmonia Solution + Nitric Acid ---> Ammonium Nitrate + WaterAmmonia Solution + Phosphoric Acid ---> Ammonium Phosphate + Water

ADVANTAGES OF FERTILISERS:1. They increase the crop yield.2. There is an increased profit for the farmers.3. Fields do not have to be left fallow.4. Previously infertile land can become fertile and be cultivated.

DISADVANTAGES OF FERTILISERS:1. Nitrate fertilisers can cause ‘blue baby syndrome’ if the nitrate ends up in drinking

water supplies (decreased oxygen carrying capacity of haemoglobin in red blood cells).

2. Fertilisers cause Eutrophication.

Fertilisers wash into rivers & streams,

Over growth of algae occurs,

Algae blocks the sunlight so plants at the bottom

of the water die,

Bacteria decompose the dead plants,

The bacteria respire - using up all the oxygen,

This suffocates & kills fish.

HOW TO MAKE A FERTILISER:1. Put ammonia solution into a

beaker and add universal indicator,2. Add sulphuric acid until the

universal indicator turns green (neutralised),

3. Add a spatula of decolourising charcoal,

4. Filter into an evaporating basin and evaporate off the water.