The short answer
The high-yield chemistry idea behind a steady stream of Section III questions.
Written and checked by GAMSAT tutors — not AI-generated.
Try the reasoning style
We treat forgetting as a failure — a lapse to be patched with reminders and records. Yet a mind that kept everything could not think; it would drown in the undifferentiated noise of every moment it had ever lived. To forget is not so much to lose information as to decide, mostly without our noticing, what was never worth keeping.
The author's argument relies most directly on which unstated assumption?
Pick an option to see how the tutor reasons to the answer — not just whether you were right.
Not quite — the answer is B.
Work backwards from the conclusion: a mind that ‘kept everything’ supposedly ‘could not think.’ That only follows if thinking means leaving most of experience out — so B is the premise the argument quietly rests on. A raises reliability, which the passage never weighs; C contradicts ‘mostly without our noticing’; D smuggles in a claim about intellect the passage never makes. The question rewards finding the hidden premise, not recalling a fact.
Chemical equilibrium is a Section III favourite — and you can answer most questions with a single principle, no memorised tables needed.
Le Chatelier in one sentence
Disturb a system at equilibrium and it shifts in the direction that partly opposes the change.
What equilibrium actually means
A reversible reaction is at equilibrium when the forward and reverse rates are equal. Concentrations stop changing, but nothing has stopped — both reactions are still running. It is dynamic, not static. For A + B ⇌ C + D the equilibrium constant is K = [C][D] / [A][B], each concentration raised to its coefficient. A large K means products are favoured; a small K means reactants are.
Predict any shift in three checks
Concentration
Add a substance → the system consumes it, shifting away from the side you added to. Remove one → it shifts to replace it.
Pressure / volume (gases)
Squeeze (raise pressure) → shifts toward the side with fewer moles of gas. Expand → toward more moles.
Temperature
Treat heat as a reactant (endothermic) or product (exothermic). Raise temperature → shifts in the endothermic direction, absorbing the heat.
Worked example
For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), ΔH is negative (exothermic). Which raises the yield of NH₃ — increasing temperature, or increasing pressure?
The catalyst trap
A catalyst speeds the forward and reverse reactions equally. It gets you to equilibrium faster; it does not move the position of equilibrium and does not change K. So any option claiming a catalyst increases the yield is wrong — it only changes how long you wait for the same yield.
Check yourself
A reaction at equilibrium is exothermic. You raise the temperature. What happens?
The paper gives you a table of equilibrium measurements and asks you to read the direction of every shift out of it — including the one that did not happen. Below is that shape.
Passage· 3 questions on it
The following is adapted from an industrial chemistry report. The compound is not one you are expected to have met.
| Run | Temperature (K) | Total pressure (kPa) | Catalyst | M converted at equilibrium (%) | Time to reach equilibrium (min) |
|---|---|---|---|---|---|
| 1 | 350 | 100 | no | 62 | 55 |
| 2 | 400 | 100 | no | 41 | 12 |
| 3 | 450 | 100 | no | 24 | 3 |
| 4 | 350 | 200 | no | 71 | 48 |
| 5 | 350 | 100 | yes | 62 | 4 |
Q1 of 3 on this passage
What do runs 1, 2 and 3 establish about the enthalpy change of the forward reaction?
Q2 of 3 on this passage
Runs 1 and 4 differ only in pressure. The rise in conversion from 62 to 71 per cent happens because
Q3 of 3 on this passage
Comparing run 5 with run 1, what did the catalyst change?
Key takeaways
- A disturbed equilibrium shifts to partly oppose the change.
- Concentration: shift away from whatever you add.
- Pressure: shift toward the side with fewer moles of gas.
- Temperature: raising it favours the endothermic direction.
Practise this with real GAMSAT-style questions
A timed diagnostic, real practice questions with worked explanations, and your first essay marked on our rubric built from ACER's two published criteria.