Chemical reactions rearrange atoms — Science, 14–17 years
In a chemical reaction, atoms are not created or destroyed; their bonds change and new substances form.
Idea
A chemical reaction is a rearrangement of atoms. The atoms present at the start remain, but old connections between them break and new connections form. Because the arrangement changes, the products can have very different properties from the starting substances.
Why it matters
People needed to explain why burning, rusting and cooking make substances that cannot simply be changed back. The idea separates a chemical change from a physical change, such as melting ice. It also gives a rule for checking equations: every kind of atom must be counted on both sides.
Worked example
For hydrogen burning, start with 2H₂ + O₂. Count four hydrogen atoms and two oxygen atoms. The product is water, H₂O, so place a 2 before it: 2H₂O has four hydrogen and two oxygen atoms. The balanced equation is 2H₂ + O₂ → 2H₂O.
Common trap
A common, understandable mistake is changing the small number in a formula to balance an equation. The small number belongs to one molecule, so changing it changes the substance: H₂O is not the same as H₂O₂. Change only the large numbers in front, which count whole molecules.
Outside school
This idea is used to design medicines, fertilisers, batteries and cleaner fuels. A food label describes substances in the food, while a recipe describes how ingredients are rearranged by heat. In factories, balancing the atoms helps control how much material is needed and how much waste is made.
Keep exploring
Other languages
Loading MyLeoNes™…