Chemical reactions — Chemistry, 11–13 years
In a chemical reaction, particles rearrange and form new substances. Signs such as a new gas, colour change or heat can give clues, while the atoms themselves are conserved.
Particles rearrange
A chemical reaction is not just mixing or changing shape. The atoms in the starting substances break old connections and make new ones, producing substances with different properties. The atoms are still there, but they have new neighbours and a new arrangement.
Why look for evidence?
A reaction happens at a scale too small for our eyes to watch directly. Chemists therefore look for changes that reveal new substances, such as bubbles, a lasting colour change, a solid forming, or temperature changing. These clues are useful, but one clue alone does not always prove a reaction.
Vinegar and bicarbonate
Put 20 mL of vinegar in a cup and add one teaspoon of bicarbonate of soda. Bubbles form immediately, showing that a gas is being made. The cup may feel cooler, and the original powders and liquid no longer behave the same way. The particles have rearranged into new substances, including carbon dioxide gas.
Bubbles are not always a reaction
Seeing bubbles can make you conclude that a chemical reaction has happened. That is reasonable, because reactions often make gases, but boiling water also makes bubbles when liquid water becomes gas. You must ask whether a new substance formed, not only whether bubbles appeared.
Reactions in everyday life
Baking, digesting food and using a battery all depend on chemical reactions. In baking, heat helps ingredients form new substances that change the mixture’s taste and texture. In a battery, reactions push electrons around a circuit, providing energy for a torch or a phone.
Keep exploring
Other languages
Loading MyLeoNes™…