Some reactions make new substances — Chemistry, 4–6 years
Sometimes substances do more than mix: they react and form something with new properties. Bubbles, a new smell or a lasting colour change can give us clues.
A reaction can make something new
When two substances react, their tiny parts can join in a new way. The result may not behave like either starting substance. Mixing sand and stones only puts them together, but vinegar and bicarbonate can react and make bubbles of a new gas.
Why tell mixing from reacting?
People needed to know whether a substance could be collected again or had changed into something else. That matters when making food, cleaning or choosing safe materials. Looking for lasting clues, such as gas or a new solid, helps us avoid treating every change as just mixing.
Vinegar and bicarbonate
Put one spoon of bicarbonate in a cup and add two spoons of vinegar. First, the powders and liquid are separate. Then bubbles appear quickly, the mixture fizzes and foam rises. The bubbles are a gas made during the reaction, so this is more than simply stirring two things together.
Bubbles do not always mean a reaction
It is reasonable to think any bubbles prove that a new substance formed. A fizzy drink already contains gas, so bubbles can simply escape when the drink is opened or stirred. We need to ask where the gas came from and whether a new substance was made, not rely on bubbles alone.
Cooking and cleaning
Reactions happen when bread rises, when a cake changes in the oven and when some cleaners remove grime. In each case, substances may gain new smells, textures or gases. At home, an adult should choose the substances and amounts: never mix cleaning products, because some reactions can make harmful gases.
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