4.10.4 The Haber process and the use of NPK fertilisers

What is the Haber process used for?

To manufacture ammonia which can be used to produce nitrogen-based fertilisers.

What are the reactants that enter the Haber process to make the ammonia?

Nitrogen and Hydrogen.

Where is the Nitrogen sourced from?

The air.

Where is the Hydrogen sourced from?

Natural gases such as methane.

Describe the Haber Process.

• First the purified gases are pumped into the compressor through pipes

• The gases are compressed to about 200 atmospheres inside the compressor

• Then the gases are pumped into a tank containing layers of catalytic iron beads at 450 degrees

• Some of the nitrogen and hydrogen react to form ammonia

• the products and unreacted reactants are then pumped into a cooling tank where the ammonia condenses and is collected and the gases are recycled back into the system.

Why is some nitrogen and hydrogen not reacted to make ammonia?

Because it is a reversible reaction and so it is likely that it reversed back to the reactants.

Why is the pressure and temperature used in the habor process used?

The pressure must be high so that the equilibrium shifts the side with less moles, which is the side of the products, this increases rate of yield. The temperature is not too high or lo because if the temperature was too high it would shift to the exothermic side of the reaction, the reactants, and if the temperature was too low the rate of reaction would be too slow, and so 450 degrees is in between.

What is the chemical formula for ammonia?

N2 + 3H2 ←→ 2NH3

Why are catalytic iron beads used?

To increase rate of reaction.

What does NPK stand for?

Nitrogen, phosphorus and Potassium.

What compounds can be found when mining?

Potassium chloride, potassium sulfate and phosphate rock.

Why can’t phosphate rock be used directly as a fertiliser?

Because it is insoluble, you must treat it with nitric acid or sulfuric acid to produce soluble salts.

Why are Nitrogen compound useful in plants?

They help them have healthier leaves, good for photsynthesis.

Why are potassium compound useful in plants?

Healthy fruit and flowers.

Why are phosphorus compound useful in plants?

promotes root growth.

Recall the names of the salts produced when phosphate rock is treated with nitric acid, sulfuric acid and phosphoric acid.

nitric acid —> Calcium nitrate and phosphoric acid

Sulphuric acid —> calcium sulfate and calcium phosphate (Single superphosphate)

Phosphoric acid —> calcium phosphate (Triple superphosphate)