Explain vs Describe vs Suggest (Chemistry Command Words)
Chemistry answers are not marked only on “being correct”. They’re marked on doing the right job for the command word.
This page teaches the 3 highest-frequency command words that silently decide marks: describe, explain, and suggest.
- Describe = what you see (data/observations).
- Explain = why it happens (cause → effect).
- Suggest = a plausible idea (supported by chemistry).
Quick Reference (What the marker wants)
| Command word | What the marker is looking for | What you should write | Common mark-loser |
|---|---|---|---|
| Describe | Trend/pattern in data or observations | “As X increases, Y decreases… from ___ to ___ (units).” | Giving reasons (“because…”) instead of evidence |
| Explain | A cause using the correct principle | “Because ___, therefore ___, so ___.” | Stating the trend again (re-describing) |
| Suggest | A plausible reason/method/improvement | “A possible reason is ___, because ___, so ___.” | Wild guesses that contradict the data |
1) How to answer Describe
Describe questions are scored by clarity and evidence. The mark scheme is usually checking: did you read the graph/table/experiment properly?
Describe checklist (use this every time)
- State the overall trend (increase/decrease/no change/levels off).
- Quote at least two values (with units) that prove the trend.
- Use comparative language (“higher than”, “lower than”, “approximately double”).
- Mention an anomaly only if it is clearly relevant.
- “As [X] increases from [value] to [value], [Y] [increases/decreases] from [value] to [value].”
- “At the start, [Y] increases rapidly, then it levels off at about [value].”
2) How to answer Explain
Explain questions want a cause that makes the observation inevitable. The highest-scoring answers read like a chain: principle → mechanism → result.
Explain checklist
- Name the driver (the real cause): particle collisions, bonding/structure, equilibrium shift, electron transfer, etc.
- Link cause to effect using because → therefore logic.
- Use key terms (mark-scheme triggers), not vague words like “it increases”.
Because [cause/driver], therefore [what changes at particle/ionic level], so [what you observe / what the data shows].
3) How to answer Suggest
Suggest means “use chemistry to propose something reasonable”. The mark scheme usually awards marks for plausibility + linkage (not for guessing a specific memorised phrase).
Suggest checklist
- Start with “A possible reason is…” or “One improvement is…”.
- Make it chemistry-consistent (no contradictions with core principles or the data).
- If it’s a practical question: name the limitation, then the improvement, then the effect.
Limitation: [what causes error / bias].
Improvement: [specific change].
Effect: this reduces [random/systematic] error / increases reliability because [why].
If you’re doing practical papers, these are high-frequency “suggest” links:
- O Level: Errors & Improvements (ACE)
- A Level: Paper 4 Skills: P, MMO, PDO, ACE
4) Mixed prompts: “Describe and explain” / “Explain, using the data”
These are two-part questions disguised as one sentence:
- Describe AND explain: do both jobs. Describe first (evidence), then explain (reason).
- Explain, using the data: quote at least one value/trend inside your explanation.
Evidence first (describe briefly) → reason second (explain) → tie-back (therefore…).
Top Exam Traps
- Writing a perfect explanation when the command word was describe (you get 0 for the wrong job).
- Using “because” without a real cause (“because it increases” is not a cause).
- Quoting data with no units, or describing without any numbers at all.
- For “suggest improvements”: writing “human error” / “be more careful” (too vague; no mechanism).
- Mixing “describe” (what changed) with “explain” (why it changed) in one messy paragraph.
Worked Examples
Attempt the question in 2–4 lines first. Then open the answer and compare your structure (not just the wording).
Worked Example 1 (Describe — graph trend)
You are given a graph of volume of gas (cm³) vs time (s) for two temperatures. Describe the difference between the two curves.
Show Answer
A correct describe answer should state the shape and compare values:
- Both curves start at 0 cm³ and increase with time, then level off at about the same final volume.
- The higher-temperature curve rises more steeply at the start (greater initial gradient), so the reaction is faster.
- It reaches the plateau earlier (shorter time to completion).
Worked Example 2 (Explain — rate and temperature)
Explain why increasing temperature increases the rate of a reaction.
Show Answer
Because particles have higher kinetic energy at higher temperature, therefore a larger fraction of collisions have energy ≥ Eₐ (activation energy), so there are more effective collisions per second and the reaction rate increases.
Worked Example 3 (Suggest — why yield is lower than expected)
In a preparation, the percentage yield is 62%. Suggest one reason why the yield is not 100%.
Show Answer
A possible reason is that some product was lost during filtration/transfer (it stuck to the container or remained on the filter paper), so the mass collected was less than the true mass produced.
Worked Example 4 (Suggest an improvement — practical)
In a calorimetry experiment, the temperature rise is smaller than expected. Suggest one improvement to obtain a more accurate temperature change.
Show Answer
Limitation: heat is lost to the surroundings.
Improvement: use an insulated cup with a lid (and stir) to reduce heat loss.
Effect: less heat escapes, so the measured temperature rise is closer to the true value (more accurate).
Worked Example 5 (Describe AND explain — observation + reason)
Magnesium ribbon is added to dilute hydrochloric acid. Describe what you observe and explain it.
Show Answer
Describe: Effervescence occurs and the magnesium ribbon gets smaller and disappears.
Explain: Because magnesium is above hydrogen in the reactivity series, therefore it displaces hydrogen from the acid, so hydrogen gas is produced: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
Next steps
- Exam Skills Hub: command words, data answers, graphs, and practical “suggest” wording.
- If you’re studying for O Level: O Level Chemistry and O Level Cheatsheet.
- If you’re studying for A Level: A Level Chemistry.
- If “suggest improvements” keeps losing you marks: Errors & Improvements (O Level) or Paper 4 Skills (A Level).