Haber Process HQ

Making ammonia 🏭

The **Haber process** is one of the most important industrial reactions in the world: it makes **ammonia** (NH3), the raw material for the fertilisers that feed billions of people. It combines two gases in a **reversible** reaction, and the exam classic is explaining why its operating **conditions are a compromise** - not simply the ones that would give the most ammonia. This module builds that answer.

The words you need 🗂️

Five terms carry the topic. Learn them before the checks lean on them.

What goes in? ⚗️

In the Haber process, which two gases combine to make ammonia?

• Nitrogen and hydrogen
• Oxygen and hydrogen
• Nitrogen and oxygen
• Carbon dioxide and hydrogen

Round the reactor 🪜

An interactive activity.

A balancing act ⚖️

The Haber reaction is **reversible**: as fast as ammonia forms, some breaks back down. In the sealed reactor it reaches **dynamic equilibrium** - the forward and reverse reactions run at the **same rate**, so the amounts of each gas stay **constant** (not equal, just steady). Because it never goes fully to completion, choosing the conditions is all about tilting that balance toward ammonia - without making the reaction too slow to be useful.

At equilibrium 🔁

In the sealed reactor, what is true once dynamic equilibrium is reached?

• The forward and reverse reactions happen at the same rate, and concentrations stay constant
• The reaction has completely stopped
• All the nitrogen and hydrogen have turned into ammonia
• The amounts of every gas are exactly equal

The temperature dilemma 🌡️

Temperature is where the compromise bites. The forward reaction is **exothermic**, so cooling favours more ammonia - but cooling also slows everything down.

Why about 450 degrees? 🎯

A lower temperature would give a higher yield of ammonia. So why is the Haber process run at a fairly high 450 degrees?

• At a low temperature the rate is far too slow, so 450 degrees is a compromise
• A low temperature would make the reaction explode
• The catalyst only works above 450 degrees
• A higher yield is not actually wanted

Pressure and the catalyst ⬇️

Two more conditions. **High pressure (about 200 atmospheres)** helps in two ways: the forward reaction turns 4 gas molecules into 2, so squeezing the gases shifts equilibrium toward ammonia (**higher yield**) and speeds the rate too. Very high pressure is costly and dangerous, so 200 atmospheres is a practical choice. The **iron catalyst** speeds the reaction up so equilibrium is reached sooner - but a catalyst changes only the **rate**, never the yield or the position of equilibrium.

Match each condition to its effect 🔗

Boost the yield ✅

Select the TWO changes that would increase the YIELD of ammonia at equilibrium.

• Increasing the pressure
• Lowering the temperature
• Adding an iron catalyst
• Increasing the temperature

Run the plant 🧭

An interactive activity.

The summary 📝

The Haber process makes ammonia from _____ and hydrogen in a reversible reaction. The conditions are a _____: high _____ raises both the yield and the rate, while an iron _____ speeds the rate without changing the yield. A temperature of about 450 degrees is chosen as a balance, because the forward reaction is _____, so a lower temperature would raise the yield but slow the reaction too much.

Your turn ✍️

An interactive activity.