Controlling Reactions in Industry and Nature
In 1909, Fritz Haber synthesised the first 100 g of ammonia from nitrogen and hydrogen at 500°C and 200 atm, unlocking a process that now feeds 4 billion people.
Printable Worksheets
Print or save as PDF, or build a custom worksheet from any module's questions.
Q1 · Why might a company making chemicals want to run a reaction at a moderate temperature rather than the hottest possible temperature?
Q2 · Your body controls hundreds of chemical reactions every second. Why do you think fever (high body temperature) can be dangerous?
● Know
- How the Haber process uses temperature, pressure and catalysts to make ammonia
- How enzymes act as biological catalysts in digestion and fermentation
- Why controlling reaction rates matters for safety and efficiency
● Understand
- That industrial processes involve trade-offs between speed, yield, cost and safety
- That living things use catalysts (enzymes) to control reactions at body temperature
- How Australian industries apply reaction rate principles
● Can do
- Explain the trade-offs in the Haber process using collision theory
- Compare industrial and biological catalysts
- Evaluate how reaction rate control benefits Australian industries
Run the Haber process at 300°C and the yield is high but the reaction is too slow to be profitable; run it at 600°C and the rate is fast but the equilibrium yield drops below 10%, industrial chemists must find the precise conditions where both speed and yield are acceptable. Controlling chemical reactions is the essence of chemical engineering. Industrial processes must balance multiple objectives: fast rate, high yield, low cost, safety, and environmental impact.
Temperature control: High temperatures increase rate but increase energy costs and may reduce yield for exothermic reactions. Insulation, heat exchangers, and cooling systems manage temperature precisely.
Pressure control: High pressure increases rate and yield for gas-phase reactions (fewer moles of gas on product side). But high-pressure equipment is expensive and dangerous. Pressure vessels must meet strict safety standards.
Catalyst selection: The right catalyst can make an impractical reaction economical. Catalyst development is a major research area. Catalyst lifetime, poisoning resistance, and regeneration methods are critical economic factors.
Biological control: Living organisms control thousands of simultaneous reactions through enzymes, pH regulation, compartmentalisation (organelles), and feedback mechanisms.
The blast furnace for iron production operates at 1,500-2,000C. Could a catalyst allow lower temperatures? The reduction of iron oxide by carbon is thermodynamically favourable at lower temperatures, but the rate would be impractically slow. No practical catalyst exists for this reaction. The high temperature is necessary for kinetics, not thermodynamics. The energy cost is enormous, which is why the steel industry is a major CO2 emitter. Research into hydrogen-based direct reduction (operating at lower temperatures) could revolutionise steel-making if renewable hydrogen becomes cheap enough.
Australian steel industry: BlueScope Steel operates the Port Kembla steelworks, Australia largest steel plant. The blast furnaces there produce over 5 million tonnes of steel annually. Engineers continuously optimise reaction conditions to maximise output while minimising energy use and emissions. BlueScope has invested in CO2 capture research and is exploring hydrogen injection into blast furnaces to reduce carbon emissions. Australian steel-making faces challenges from cheaper imports, but remains strategically important for construction and defence.
There is always a single best set of conditions for any reaction. This is false. The optimal conditions depend on what you are optimising for. If you want maximum rate, use high temperature and catalyst. If you want maximum yield for an exothermic reaction, use low temperature. If you want minimum cost, you might accept lower rate and yield. If you want minimum environmental impact, you might choose a less efficient but cleaner process. Optimisation is multi-objective, and different stakeholders will prefer different solutions.
Match each industrial process to its key control strategy.
Modern chemical plants use sophisticated engineering to maximise efficiency and safety.
Batch vs continuous processes: Batch processes mix reactants in a vessel, let the reaction proceed, then isolate products. They are flexible and suit small-scale or varied production. Continuous processes pump reactants through reactors continuously, with products removed at the same rate. They are more efficient for large-scale production of a single product.
Recycling: In many reactions, reactants are not completely converted to products in a single pass. Unreacted material is separated and recycled back to the reactor. This improves atom economy and reduces waste.
Heat integration: Exothermic reactions release heat; endothermic reactions require heat. Heat exchangers transfer heat from hot product streams to cold reactant streams, reducing external heating and cooling requirements.
Safety: Exothermic reactions can run away if heat is not removed quickly enough. Temperature rises -> rate increases -> more heat released -> temperature rises further. This positive feedback can cause explosions. Emergency cooling, quench systems, and pressure relief valves are essential safety features.
The Bhopal disaster (1984) involved a runaway reaction in a pesticide plant. Water entered a methyl isocyanate storage tank, initiating an exothermic reaction. The refrigeration system was turned off to save money, so heat could not be removed. Temperature and pressure rose uncontrollably, rupturing the tank and releasing toxic gas that killed thousands. This tragedy illustrates how ignoring reaction control fundamentals - temperature management, contamination prevention, and safety systems - can have catastrophic consequences. Modern chemical plants have multiple redundant safety systems to prevent similar events.
Australian process safety: The Centre for Process Safety at Curtin University works with Australian chemical companies to develop safer process designs. Their research includes early warning systems for runaway reactions, safer chemical storage methods, and inherently safer process design principles. Australian regulations require major hazard facilities to demonstrate control of reaction risks through safety management systems audited by state authorities.
Chemical plants are dangerous because chemists do not understand the reactions. This is false. Chemical engineers deeply understand the reactions they run. Accidents typically occur when safety systems fail, procedures are violated, or unexpected conditions arise (contamination, equipment failure, extreme weather). The challenge is not understanding the chemistry but reliably controlling it at scale, 24/7, for decades, with imperfect equipment and human operators. Safety engineering is about managing residual risk, not eliminating it entirely.
Biological systems are masterpieces of reaction control. A human cell runs thousands of simultaneous reactions with extraordinary precision.
Enzyme regulation: Enzymes can be switched on or off by inhibitors, activators, phosphorylation, or gene expression. This allows cells to respond to changing conditions.
Compartmentalisation: Different reactions occur in different organelles. The mitochondria run oxidative reactions; the lysosome runs hydrolysis reactions at acidic pH. Separating incompatible reactions prevents unwanted side reactions.
Feedback inhibition: When a metabolic pathway produces enough product, the product inhibits the first enzyme in the pathway. This negative feedback prevents wasteful overproduction. It is like a thermostat that turns off the heater when the room is warm enough.
Temperature regulation: Warm-blooded animals maintain body temperature within a narrow range, keeping enzyme activity optimal. Extreme environments require special adaptations - antifreeze proteins in Antarctic fish, heat-shock proteins in desert organisms.
Glycolysis, the breakdown of glucose, is regulated at three key points. The enzyme phosphofructokinase is inhibited by ATP (the product of respiration) and activated by AMP (a sign of low energy). When the cell has plenty of ATP, glycolysis slows down, conserving glucose. When ATP is depleted, glycolysis speeds up, producing more ATP. This feedback system maintains cellular energy balance automatically. Understanding these control mechanisms is essential for treating metabolic diseases like diabetes, where glucose regulation fails.
Australian metabolic research: The Garvan Institute in Sydney studies metabolic regulation in health and disease. Their research on insulin signalling and glucose metabolism has led to new treatments for type 2 diabetes. Australian scientists have discovered novel enzymes and metabolic pathways in native organisms, including unique adaptations in marsupials and venomous snakes. These discoveries expand our understanding of biochemical diversity and may lead to new industrial enzymes or pharmaceuticals.
Biological reactions are completely different from industrial reactions. This is false. The same chemical principles apply in both contexts. Enzymes are catalysts; metabolic pathways are industrial pipelines scaled down to molecular dimensions. The main differences are that biological systems use aqueous conditions, mild temperatures, and highly specific catalysts, while industry often uses high temperatures, organic solvents, and metal catalysts. But the underlying chemistry - bond breaking and forming, energy changes, rate control - is identical. Biomimicry in chemical engineering seeks to replicate biological efficiency in industrial processes.
Tap each card to flip. Mark Got it when you can recall the answer without flipping.
Wrong: "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.
Right: The Haber process uses a compromise temperature of about 450 °C, high enough for an acceptable rate but not so high that the equilibrium shifts to reduce yield. The iron catalyst makes this moderate temperature workable, balancing rate and yield economically.
Wrong: "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.
Right: Enzymes are biological catalysts and, like all catalysts, are not consumed in the reaction. A single enzyme molecule can catalyse thousands of reactions per second, though they can be permanently destroyed by high temperature or extreme pH.
Wrong: "Fermentation is faster at any high temperature." No � fermentation is fastest around 30–40 °C for most yeasts. Above about 50 °C the enzymes in yeast are denatured and fermentation stops.
Right: Fermentation has an optimal temperature range of about 30–40 °C for most yeasts. Above roughly 50 °C, the yeast enzymes denature and fermentation ceases completely, higher temperature is not better once you exceed the enzyme's tolerance.
Australian Mining and Agriculture
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.
✍ Copy Into Your Books
▾Haber Process
- Nitrogen + Hydrogen → Ammonia
- High temperature, high pressure, iron catalyst
- Trade-off: speed vs yield vs cost vs safety
Enzymes
- Biological catalysts (proteins)
- Speed up reactions at body temperature
- Specific to one substrate (lock and key)
- Denatured by extreme heat or pH
Fermentation
- Glucose → Ethanol + CO₂
- Catalysed by yeast enzymes
- Temperature-controlled for quality
Explain the Trade-Off
Compare Industrial and Biological Catalysts
At the start of this lesson, the hook told you about the Haber process, ammonia made at exactly 450°C and 200 atmospheres, not the hottest or highest possible, but the "sweet spot" that balances speed and yield and feeds roughly half the world's population.
Now that you understand how temperature, pressure, and catalysts are all being balanced in industrial processes, can you explain in your own words why the Haber process doesn't just use the highest possible temperature? How has your thinking about "optimising" a reaction changed from when you first read that hook?
Q1. 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
Q2. 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
Q3. 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
Revisit Your Thinking
Go back to your Think First answer. Has your understanding changed?
- Can you now explain why 450 °C is a compromise in the Haber process?
- How do enzymes solve the temperature problem that industry faces?
Model answers (click to reveal)
Answers
▾MCQ 1
BThe 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.
MCQ 2
CAn 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.
MCQ 3
AAt 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.
MCQ 4
DIndustrial 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.
MCQ 5
BModerate 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.
Short Answer 1
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.
Short Answer 2
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.
Short Answer 3
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.