The Haber process and NPK fertilisers

What is the Haber Process used for?

It is used to manufacture ammonia from nitrogen and hydrogen.

What is ammonia used for?

Ammonia is mainly used to make fertilisers.

explain how the haber process works

The purified gases are passed over a catalyst of iron at a high temperature (about 450°C) and a high pressure (about 200 atmospheres). Some of the hydrogen and nitrogen reacts to form ammonia. The reaction is reversible so some of the ammonia produced breaks down into nitrogen and hydrogen:

nitrogen +hydrogen ⇌ammonia

What is the word equation for the Haber Process?

Nitrogen + Hydrogen ⇌ Ammonia

What is the balanced symbol equation for the Haber Process?

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Why is the Haber Process a reversible reaction?

Ammonia can break down back into nitrogen and hydrogen.

Where does the nitrogen come from?

The air (which is 78% nitrogen).

Where does the hydrogen come from?

Reacting methane with steam (from natural gas).

Conditions for the Haber Process

Condition	Value Used	Why This Value?

Temperature

450°C

High enough for a fast reaction but not too high to reduce ammonia yield.

Pressure

200 atmospheres (200 atm)

Increases ammonia yield (favours forward reaction) without being too expensive/dangerous.

Catalyst

Iron

Speeds up the reaction without affecting yield.

What does the iron catalyst do?

It speeds up both forward and backward reactions so equilibrium is reached faster.

How is ammonia separated from the unreacted gases?

✅ Ammonia condenses into a liquid when cooled.
✅ Unreacted nitrogen and hydrogen are recycled back into the reactor.

What are NPK fertilisers?

Fertilisers that contain Nitrogen (N), Phosphorus (P), and Potassium (K) to help plants grow.

Why are fertilisers important?

✅ Increase crop yield.
✅ Replace nutrients removed by previous crops.

How is nitrogen supplied in fertilisers?

From ammonia, which is used to make ammonium nitrate (NH₄NO₃).

How is ammonium nitrate made?

Ammonia + Nitric Acid → Ammonium Nitrate
NH₃ + HNO₃ → NH₄NO₃

How is phosphorus supplied in fertilisers?

From phosphate rock, which must be treated because it is insoluble.

What acids are used to treat phosphate rock and what salts do they form?

• Nitric acid → phosphoric acid and calcium nitrate are produced

  • The phosphoric acid  is neutralised with ammonia forming ammonium phosphate

• Sulfuric acid → Produces single superphosphate. ( a mixture of calcium phosphate and calcium sulfate)

• Phosphoric acid → Produces triple superphosphate. ( calcium phosphate)

How is potassium supplied in fertilisers?

From potassium chloride (KCl) or potassium sulfate (K₂SO₄), both of which are soluble and can be used directly.

why must fertiliser compounds be soluble in water

so they can be absorbed by the root hair cells: