To explain a concept with an example, state the idea, describe one case, then say how the case shows the idea. The third step is the one students skip.
This lesson is part of SPM subjects and learning resources. Reading it after separating observation from explanation helps, because both skills ask for reasoning in full sentences.
What does a good concept-and-example answer contain?
Use four short steps. The labels are a memory aid, not headings to write in the exam.
- Concept. One sentence that names the idea and what it says.
- Example. One specific case, with real details.
- Link. One sentence beginning “This shows that…” or “So…”.
- Result. What changes or what you would measure.
Two or three sentences can carry all four steps if each one does a single job.
Worked example: surface area and rate of reaction
Question (original): Explain how surface area affects the rate of a reaction, using an example. [3 marks]
Answer. A larger surface area increases the rate of reaction because more particles of the solid are exposed to collide with the other reactant. For example, 5 g of powdered calcium carbonate reacts with dilute hydrochloric acid faster than a 5 g lump of the same chalk. The powder exposes far more surface, so there are more collisions per second and carbon dioxide is released more quickly.
Mark it against the four steps. The concept is the first sentence. The example is the second. The link is “so there are more collisions per second”, and the result is faster gas release.
The mistake that costs marks
A weak answer gives the example but leaves the link out: “Powdered chalk reacts faster than a lump.” This is true, but it is only an observation. The marker cannot see that you understand why.
| Part | Weak answer | Stronger answer |
|---|---|---|
| Concept | (missing) | Larger surface area exposes more particles |
| Example | Powder reacts faster than a lump | 5 g powder against a 5 g lump of the same chalk |
| Link | (missing) | More collisions per second, so a higher rate |
The fix is to write the link sentence on purpose. If you cannot finish “This shows that…”, the example is not yet doing its job.
Choosing an example you can defend
A good example has three features. It is specific, so name the substances or objects. It is fair, so the comparison changes only one thing. It is checkable, so you can say what would be measured.
In the chalk case, the mass and the acid are the same, and only the form changes. That is what makes it a fair test of surface area.
Check yourself
Explain the idea that pressure depends on area, using an example such as cutting with a knife. [3 marks]
Answer
Pressure is force divided by the area over which it acts. A sharp knife has a very thin edge, so the same push from your hand acts on a tiny area. For example, pressing with 20 N on an edge of 0.0002 m² gives 100 000 Pa, far greater than the same push on a blunt edge of 0.002 m², which gives 10 000 Pa. The greater pressure cuts the food.
The calculation checks out: 20 ÷ 0.0002 = 100 000 and 20 ÷ 0.002 = 10 000. The link is the comparison of the two pressures for the same force.
What to study next
Try the original mixed practice set and apply the four steps to each explain question. The structured answer self-review tool gives you a checklist for reading your own answers.
For help choosing examples across the syllabus with a teacher, see online one-to-one Additional Science tuition.