Chemical reactions do not just happen in test tubes. Farmers need fertiliser, breweries need beer, miners need safe extraction — and all of them depend on controlling reaction rates. In this lesson you will discover how industry and living things use temperature, pressure and catalysts to make reactions happen exactly when and how they are needed.
Australia produces over 30 million tonnes of wheat each year. To grow this wheat, farmers need nitrogen fertiliser. The most common way to make this fertiliser is the Haber process, which combines nitrogen gas from the air with hydrogen gas to make ammonia.
Write down your answers before reading on:
Balancing speed, yield and cost in industry
The Haber process is one of the most important industrial chemical reactions on Earth. It converts nitrogen gas (N₂) from the air and hydrogen gas (H₂) into ammonia (NH₃), which is used to make fertilisers that feed billions of people.
The reaction needs three conditions to proceed at a useful rate:
At very high temperatures the reaction is fast, but the yield drops because the reverse reaction (ammonia breaking down) also speeds up. At lower temperatures the yield is better, but the reaction is too slow to be economically viable. The iron catalyst solves this by making the reaction fast enough at a moderate temperature where the yield is still acceptable.
Nature's precision reaction controllers
Living things cannot use high temperatures or crushing pressures to speed up reactions. Instead, they use enzymes — specialised protein molecules that act as biological catalysts. Enzymes allow complex reactions to occur rapidly at body temperature.
In the human digestive system:
Each enzyme is shaped to fit a specific molecule (its substrate) like a lock and key. This specificity means enzymes control exactly which reactions happen and when. Unlike industrial catalysts, enzymes can be damaged by temperatures that are too high or pH levels that are too extreme.
Fermentation is another biological process controlled by enzymes. Yeast cells contain enzymes that convert glucose into ethanol and carbon dioxide:
Glucose → Ethanol + Carbon dioxide
This reaction is slow at low temperatures, fast at moderate temperatures, and stops if the temperature gets too high because the yeast enzymes are denatured. Brewers and winemakers carefully control temperature to get the right rate of fermentation and the desired flavour.
Why reaction rate control saves lives and money
Controlling reaction rates is not just about making products faster — it is often about preventing disasters. Uncontrolled reactions can cause explosions, fires and toxic releases.
In industry, engineers use several strategies:
Australia's mining industry uses controlled leaching reactions to extract metals from ore. The rate must be fast enough to be profitable but slow enough to be safe and environmentally responsible. In food production, Australian dairy and wine industries rely on precisely controlled fermentation temperatures to ensure product quality and food safety.
"The Haber process uses the highest possible temperature to make ammonia fastest." No — it uses a compromise temperature (about 450 °C) because extremely high temperatures reduce yield by favouring the reverse reaction. The catalyst makes the reaction fast enough at this moderate temperature.
"Enzymes are used up in the reactions they catalyse." No — like all catalysts, enzymes are not used up. They can catalyse the same reaction many thousands of times, though they can be denatured by extreme heat or pH.
Australia is one of the world's largest exporters of wheat, beef and minerals. All of these industries depend on controlled chemical reactions. The Pilbara region in Western Australia produces enormous quantities of iron ore, which is extracted using controlled leaching and reduction reactions.
Australia's wheat belt stretches across NSW, Victoria, South Australia and Western Australia. The fertilisers that sustain this production are made using ammonia from the Haber process. Australian scientists are now researching "green ammonia" made using renewable energy and hydrogen from water electrolysis, which could make Australian agriculture more sustainable while maintaining the reaction rate control that makes the process viable.
1. Why does the Haber process use an iron catalyst?
2. Which of the following best describes an enzyme?
3. A winemaker in the Barossa Valley notices that fermentation has stopped during a heatwave when temperatures reached 45 °C. What is the most likely explanation?
4. A factory manager must choose between two processes to make the same product. Process A is fast but requires 800 °C and expensive safety equipment. Process B is slower but runs safely at 200 °C with a catalyst. Which statement best evaluates the trade-off?
5. Which combination of factors would MOST increase the rate of the Haber process reaction while keeping it economically viable?
1. Explain why the Haber process uses a compromise temperature rather than the highest possible temperature. In your answer, refer to both reaction rate and yield. 4 MARKS
2. Describe how enzymes in the human digestive system control reaction rates. Use at least two named enzymes and their substrates in your answer. 4 MARKS
3. Evaluate the importance of reaction rate control for ONE Australian industry (mining, agriculture or food production). Give specific examples of how controlling reaction rates affects safety, efficiency or product quality. 4 MARKS
Go back to your Think First answer. Has your understanding changed?
B — The iron catalyst speeds up the reaction without being used up, allowing the process to run fast enough at a moderate temperature where the yield of ammonia is still acceptable. It does not increase the total possible yield or prevent decomposition.
C — An enzyme is a biological catalyst — a protein that speeds up chemical reactions in living organisms. It is not consumed, not a bacterium, and not a product of protein breakdown.
A — At 45 °C, yeast enzymes are denatured — their shape is destroyed and they can no longer catalyse fermentation. This is the most likely explanation for fermentation stopping during a heatwave.
D — Industrial decisions always involve trade-offs. The manager must consider not just speed or safety in isolation, but the balance of production rate, safety, energy costs and capital expenditure on equipment.
B — Moderate temperature with a catalyst gives a good reaction rate without destroying yield. High pressure increases collision frequency and improves yield. This combination is the actual approach used in the Haber process.
Model answer: The Haber process uses a compromise temperature of about 450 °C because higher temperatures would speed up the reaction but reduce the yield. At very high temperatures, particles have more energy, so the reaction between nitrogen and hydrogen is faster. However, the ammonia product also breaks down more easily at high temperatures, shifting the equilibrium back towards reactants. The iron catalyst allows the reaction to proceed fast enough at 450 °C, where the yield is still reasonable. This is a trade-off between speed and yield.
Model answer: Enzymes are biological catalysts that speed up specific reactions in the digestive system at body temperature. Amylase, found in saliva, catalyses the breakdown of starch into sugars. Protease, found in the stomach, catalyses the breakdown of proteins into amino acids. Lipase, in the small intestine, breaks down fats into fatty acids and glycerol. Each enzyme has a specific shape that fits only its substrate, allowing precise control over which reactions occur and when. Without enzymes, these reactions would be too slow to support life.
Model answer: In Australian mining, reaction rate control is critical for both safety and efficiency. For example, when extracting gold using cyanide leaching, the reaction rate must be controlled to maximise gold recovery while minimising the risk of toxic cyanide spills. If the reaction is too fast, heat can build up and dangerous gases may form. If too slow, the operation becomes uneconomical. CSIRO has developed controlled leaching methods that optimise reaction rates while reducing environmental impact, making Australian mining both safer and more efficient.
Master the art of reaction control! Balance temperature, pressure and catalysts to keep your factory running while avoiding disasters. Blast through platforms and show your industrial chemistry skills!
Tick when you have finished all activities and checked your answers.