Haber Hustle

Haber Hustle: run an ammonia plant and find the Haber process compromise

This free game is part of our AQA GCSE Chemistry (8462) course for exams in EXAM YEARS 2027-2029.

The Haber process for AQA GCSE Chemistry

AQA GCSE Chemistry (8462) spec point 4.10.4.1 is about the Haber process, which is used to manufacture ammonia for nitrogen-based fertilisers. You need to recall where the raw materials come from, the conditions used, what happens to the ammonia and the unreacted gases and, for Higher tier, why those conditions are a compromise. Written down, the compromise is one sentence. It only really makes sense when you see the rate and the amount of ammonia pulling in opposite directions.

In Haber Hustle you are the operator at Northfield Ammonia Works. You hook up the raw materials, take the controls and keep the plant making money. Every tanker of ammonia you fill drives off to the fertiliser works, and the farm fields behind the plant turn green.

Raw materials, conditions and recycling

Part 1 starts the plant. You click where the nitrogen comes from (the air, about four-fifths nitrogen) and where the hydrogen comes from (natural gas, mainly methane). Choosing the air for hydrogen is a common exam mistake, and the game explains why. The purified gases are compressed to about 200 atmospheres and passed over an iron catalyst at about 450 °C.

Glass pipes show the molecules flowing: blue nitrogen, white hydrogen and violet ammonia. Only about one dot in four leaving the reactor is ammonia, because the reaction is reversible: nitrogen + hydrogen ⇌ ammonia. You hold COOL on the condenser and the ammonia liquefies and is removed. Then you choose what happens to the leftover gas. Vent it and the flare stack burns off the raw materials you paid for. The right answer is to recycle the unreacted nitrogen and hydrogen back into the reactor.

Temperature: rate against the position of equilibrium

Part 2 hands you the temperature. The forward reaction is exothermic, so a lower temperature moves the equilibrium towards ammonia. Cool the reactor to 350 °C and the live graph shows a higher percentage of ammonia at equilibrium, but the reaction crawls, the tank hardly fills and the tankers give up waiting. Heat it to 550 °C and everything races, but the equilibrium moves back towards nitrogen and hydrogen and you make less. The profit line peaks around 450 °C: a reasonable amount of ammonia at a reasonable rate.

A magnified window inside the reactor shows the dynamic equilibrium: nitrogen and hydrogen joining into ammonia on the iron, and ammonia breaking back down. When the forward and reverse counters match, the reaction is at equilibrium. The reactor also warms itself up, because making ammonia gives out heat, so you have to keep the temperature in check.

Pressure, the catalyst and cost

Part 3 adds the pressure. There are 4 molecules of gas on the left of the equation and 2 on the right, so a higher pressure moves the equilibrium towards ammonia and speeds up the reaction. Push it to 300 atmospheres and the running costs shoot up: very high pressures need thick, strong pipes and powerful pumps, which are expensive and more dangerous. That is why about 200 atmospheres is used.

Part 4 is a 100-second shift where things go wrong. The catalyst is taken out, and you see the rate collapse while the percentage of ammonia at equilibrium stays the same, because a catalyst speeds up the reaction without changing the position of equilibrium. Energy prices double, a cold night cools the reactor, and the recycle valve jams open to the vent. Your score is your profit, so you feel how the conditions depend on the cost of energy and raw materials.

About 8 minutes, made for revision and classrooms

The first part has no clock and a guided first move, and each new control arrives with a short demo. Mistakes, such as the wrong raw material or holding the reactor too cold, too hot or at too high a pressure, cost money and come with a clear explanation and a link to the lesson. Five quick checks, including a graph to read, test the exam points. The results screen gives you a rank and a recap of the whole topic. It works with a mouse, touch screen or keyboard, is readable on a projector and saves your best profit.