01What happens in a chemical reaction
In a chemical reaction, bonds between atoms in the reactants break, and new bonds form to make the products. The atoms are rearranged, not lost or created.
02Signs of a chemical reaction
Not every change is a chemical reaction. Clues that a chemical reaction has happened include:
- A colour change
- A gas produced (bubbles)
- A temperature change (gets hot or cold)
- A precipitate forms (a solid appears in a liquid)
- Light or a flame is produced
03Conservation of mass
The Law of Conservation of Mass says that in a chemical reaction, no atoms are created or destroyed — so the total mass of reactants equals the total mass of products.
04Word equations
A word equation shows the reactants turning into products using an arrow (meaning 'produces' or 'reacts to form').
05Exothermic and endothermic reactions
An exothermic reaction releases energy to the surroundings, so the temperature increases (e.g. combustion).
An endothermic reaction absorbs energy from the surroundings, so the temperature decreases (e.g. some cooking-soda reactions).
| Term | 한국어 | Meaning |
|---|---|---|
| reactant | 반응물 | A starting substance in a chemical reaction |
| product | 생성물 | A new substance formed by a chemical reaction |
| precipitate | 침전물 | A solid that forms out of a liquid during a reaction |
| conservation of mass | 질량 보존 | Mass of reactants = mass of products |
| exothermic | 발열 반응 | A reaction that releases energy (gets hotter) |
| endothermic | 흡열 반응 | A reaction that absorbs energy (gets colder) |