- chemical reactions are vital for life and technology
- chemists use the words reactants to describe what they have at the start of a reactions and products to describe what they have at the end
- learn about four reactions that improved people’s lives thousands of years ago
- a chemical reaction has happened only if at least one new substance is made
- there are six indications that a chemical reaction may have happened
- test your knowledge with our questions and answers
How important are chemical reactions?
Long ago, people discovered that:
Every living thing is like a remarkably well-organized, highly sophisticated, self-managing chemistry set.
Furthermore, our high tech society would be impossible without our ability to control chemical reactions – the screen you’re viewing right now is just one example of a device that would be impossible to make.
So, on a one to ten scale of scientific importance, chemical reactions rate eleven ten.
People started reacting chemicals a long time agoOur ancient ancestors learned:
- How to harness and control the reaction between oxygen and wood to make fire.
- How to release metals from their ores. This enabled them to make efficient plows, axes, hammers and chisels.
- How to disinfect/fumigate rooms and buildings with the gas released by burning sulfur (sulfur dioxide).
- How to convert limestone into what we now call calcium oxide. Complex, large-scale construction projects such as ancient Rome’s Colosseum became possible, because calcium oxide is the basis of cement and concrete.
Not all uses were peaceful
Our ancestors used new materials, such as iron and steel, to wage war. They discovered explosive chemical reactions and made gunpowder by mixing potassium nitrate, carbon, and sulfur.
We’re still making new discoveries
Although we know a lot more about chemistry than our ancestors did, we continue to study chemical reactions, because this leads to improvements in our technology and our health.
The sheer excitement of making new discoveries also drives chemists to continue investigating reactions.
- Lithium reactions power our phones, tablet computers and cameras.
- Biochemical and electrochemical reactions allow our brains to think and store memories.
- Reactions to produce new antibiotics are needed, because some bacteria are becoming resistant to the antibiotics we’re using today.
Reactants and Products
When chemists talk about reactions, they describe the stuff they begin with as reactants and the stuff they end up with as products.
In all chemical reactions:
For example, we can make water by reacting hydrogen with oxygen.
The reactants are hydrogen and oxygen. The product is water.
How do we know there’s been a chemical reaction?
There has been a chemical reaction only when one or more new substances are made. Sometimes this is obvious, sometimes less so.
You will also often detect an energy change, because the reaction will heat up or cool down.
Food can react chemically with oxygen. Two ways of reacting food with oxygen are burning and respiration.
If the food is a carbohydrate, the word equation for both burning and respiration is:
Burning: The ash and flame make it obvious that new substances are being made and that energy has been released. Ash forms because food usually doesn’t burn cleanly. Although the carbon dioxide and water formed by the reaction are less obvious, the ash and flame make it easy to tell that a chemical reaction has taken place.
Respiration: The evidence for a chemical reaction during respiration is more subtle than when we burn food. It’s not obvious that water and carbon dioxide are made by the reaction, although we can detect them. For example, we can use limewater to show that there is more carbon dioxide in the air we breathe out than in the air we breathe in. Breathing on a cold window produces condensation, indicating water is present in our breath. The energy released by respiration keeps all animals on our planet moving and keeps warm-blooded animals warm.
Signs of a chemical reaction
Look for one or more of these:
|Gas is released|
|A solid appears or disappears|
|There is a color change|
|The temperature changes|
|Sound is heard|
The signs above are all clues, but (except for flames) don’t prove there has been a reaction.
A chemical reaction has happened only if one or more new substances are made.
When water freezes, has there been a chemical reaction? Why?Show Answer
You toast some bread and end up burning it. Has there been a chemical reaction? Why?Show Answer
A tree grows a little higher. Has there been a chemical reaction? Why?Show Answer
Name three visual clues that a chemical reaction might have happened.Show Answer
Here is an example of a chemical reaction. Identify the reactant(s) and the product(s).
The reactants are sodium and chlorine. The product is sodium chloride.