Reactions in Everyday Life
In 2022, Australia's 130-year-old Kalgoorlie gold mines produced about 300 tonnes of gold using chemical reactions — the same reactions that make your car battery and sourdough bread work.
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● Know
- Chemical reactions happen all around us — in kitchens, cars, gardens, and inside our bodies.
- Cooking, breathing, rusting, burning and digestion are all chemical reactions.
- Some reactions are fast (combustion) and some are slow (rusting, weathering).
● Understand
- Most reactions involve a transfer of energy — in or out.
- We use reactions to make food, materials, fuels and medicines.
- The same evidence rules apply: new substances, observable clues.
● Can do
- Identify reactions happening in a kitchen, garage or body.
- Classify everyday reactions as fast or slow, exothermic or endothermic.
- Explain what reactants and products were involved.
Leave a slice of bread in a warm, humid room for 3 days and watch green-grey mould appear; bite into a freshly baked loaf and smell the warm CO₂ bubbles rising from yeast fermentation; watch iron garden furniture turn orange over a wet winter. None of those things look like reactions, yet each one produces at least one brand-new substance. Chemical reactions are happening all around you, often disguised as ordinary events. Photosynthesis in plants converts carbon dioxide and water into glucose and oxygen using sunlight energy. Cellular respiration in your cells does the reverse: it breaks down glucose using oxygen to release energy for movement, growth, and repair. Combustion is a rapid reaction between fuel and oxygen that releases heat and light. Fermentation is a slower reaction used in baking, brewing, and making yoghurt.
These reactions share a common feature: they all produce new substances with different properties from the reactants. Identifying a chemical reaction means looking for evidence such as gas production, colour change, temperature change, or the formation of a precipitate.
When yeast ferments sugar in bread dough, it produces carbon dioxide gas. The tiny bubbles of gas get trapped in the dough, causing it to rise. The alcohol produced evaporates during baking, leaving behind light, fluffy bread with a completely different texture and taste from the raw ingredients.
Indigenous burning practices across Australia demonstrate a sophisticated understanding of combustion. Controlled cool burns reduce fuel loads and promote biodiversity by carefully managing temperature and flame intensity — an application of chemistry that has sustained Australian landscapes for tens of thousands of years.
Many students think photosynthesis only happens during the day and stops at night. While the light-dependent reactions do need sunlight, plants respire continuously, day and night. Photosynthesis and respiration are opposite processes, but they run in parallel rather than taking turns.
Your body is a bustling chemical factory. Cellular respiration releases energy from glucose in every living cell, powering everything from thinking to running. It is not the same as breathing. Breathing is the physical act of moving air in and out of your lungs; respiration is the chemical reaction that happens inside cells.
Digestion is another series of chemical reactions. Enzymes in your saliva, stomach, and intestines break down large food molecules into smaller units that can be absorbed into the bloodstream. Batteries use electrochemical reactions to convert chemical energy into electrical energy, while rusting is a slow chemical reaction between iron, oxygen, and water.
During a sprint, your leg muscles demand enormous amounts of energy. Cellular respiration speeds up, consuming glucose and oxygen faster than usual. You breathe heavily not to create energy, but to supply more oxygen and remove the extra carbon dioxide produced by the reaction.
CSIRO sports scientists study energy release in human muscles during exercise. By understanding the chemistry of respiration and fatigue, they help Australian athletes optimise training and recovery, translating classroom biochemistry into Olympic medals.
A persistent myth is that breathing and cellular respiration are the same thing. They are related but fundamentally different. Breathing is mechanical — moving gases in and out. Respiration is chemical — breaking glucose bonds to release stored energy. You can hold your breath and still respire for a short time using stored oxygen.
Rusting is one of the most familiar chemical reactions in everyday life. It occurs when iron reacts with oxygen and water to form iron oxide — a flaky, reddish-brown solid that weakens the original metal. The reaction is slow, but over months or years it can destroy bridges, cars, and ships unless preventive measures are taken.
Corrosion is the general term for the chemical breakdown of metals. Scientists and engineers prevent it by painting, galvanising, oiling, or using sacrificial anodes. Each method works by blocking oxygen or water from reaching the metal surface, or by providing a more reactive metal that corrodes first.
The Sydney Harbour Bridge is protected from rust by a continuous maintenance program. Workers repaint the steel structure regularly to seal it from moisture and oxygen. Without this protection, the iconic bridge would slowly weaken as iron atoms reacted with the salty harbour air.
BlueScope Steel invests heavily in anti-corrosion research for Australian conditions. The combination of coastal salt spray, humidity, and industrial pollution creates some of the world's most aggressive rusting environments, making corrosion science critical for infrastructure longevity.
Some students think rust is just surface dirt that can be wiped off. It is not. Rust is a new chemical substance — iron oxide — with different properties from pure iron. Once rust forms, the underlying metal is permanently lost and must be replaced or repaired.
Distinguishing chemical from physical changes is a vital skill. A chemical change produces new substances with different chemical properties. A physical change only alters the form or state of a substance without creating anything new. Baking a cake is chemical because heat triggers reactions that produce new flavours and textures. Cutting an apple is physical because the pieces are still apple. Rusting a nail is chemical because iron becomes iron oxide. Melting butter is physical because it can be solidified again unchanged.
Look for the clues: colour change, gas production, temperature change, precipitate formation, or a new smell. These are strong evidence that a chemical reaction has occurred.
When you bake a cake, the baking powder reacts with moisture and heat to produce carbon dioxide gas. The gas bubbles expand in the batter, creating the spongy texture. You cannot un-bake a cake and recover the original ingredients — the change is irreversible because new substances have formed.
Scientists at the Australian Synchrotron use powerful X-rays to study chemical changes in materials at the atomic level. Their research helps develop better batteries, stronger alloys, and more effective catalysts — all by understanding how and why substances transform.
Many students assume that any change involving heat is combustion. This is not true. Combustion is a specific reaction with oxygen that produces new substances such as carbon dioxide and water. Melting chocolate in the sun involves heat but is only a physical change — the chocolate is still chocolate when it cools.
You eat a sandwich. The carbohydrates in the bread undergo cellular respiration in your cells. Predict the products and where the energy goes.
How close was your prediction?
Nice calibration — your intuition is good for this kind of problem.
Good — being surprised is the point. This answer is worth remembering.
Chemistry is not confined to laboratories; it is the engine of everyday life. Every breath you take depends on cellular respiration. Every meal you eat is broken down by digestive enzymes. Every battery in your devices relies on electrochemical reactions. Understanding these processes helps you make informed decisions about health, energy, and the environment.
The key takeaway is that chemical reactions are identified by the formation of new substances. Once you know what to look for — gas bubbles, colour shifts, temperature changes, or new smells — you will start seeing chemistry everywhere.
Combustion and cellular respiration are remarkably similar at the chemical level. Both combine a fuel with oxygen to produce carbon dioxide, water, and energy. The difference is speed and control: combustion is rapid and releases energy as heat and light, while respiration is slow, controlled, and captures energy as ATP for cellular work.
The Bureau of Meteorology monitors the chemical composition of bushfire smoke to predict air quality and health impacts. Understanding combustion chemistry helps emergency services warn communities and plan evacuations during Australia's fire season.
Some students believe chemical reactions only happen in laboratories with beakers and Bunsen burners. Nothing could be further from the truth. The most important chemical reactions on Earth — photosynthesis, respiration, digestion, and decomposition — happen in forests, oceans, kitchens, and your own body every second.
At the start of this lesson, you considered how the same type of chemical reaction that extracts gold from rock in Kalgoorlie also powers the battery in a car.
Now that you've connected chemical change to real industries, how has your sense of why this topic matters shifted? Did anything surprise you about the scale or variety of applications?
1. Which gas is produced during photosynthesis?
2. What type of reaction occurs inside a battery to produce electricity?
3. Which of the following is an example of fermentation?
4. What are the reactants in cellular respiration?
5. Why is rust considered an example of corrosion?