S5 Chemistry: Industrial Processes (Paper 4: Misconception Drill)

2026-11-12

Ten items on the commonest industrial process misconceptions: catalyst and yield, exothermic heating, where pressure helps, recycling and cost, with answers.

Direct answers　Answers in order: a catalyst does not change the yield, it is exothermic so heating lowers the yield, the two processes differ, yield falls and rate rises, 75.0 per cent, 23 kJ, about 87.04 per cent, every atom ends up in ammonia so 100 per cent, 34 g by conservation of mass, compression and heating costs also count.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: S5 Chemistry: Industrial Processes
Level	S5

02　Questions (10 items)

FoundationDoes a catalyst change the equilibrium yield?
FoundationIs 450 degrees C used in the Haber process because the reaction is endothermic and therefore needs heating?
FoundationIs raising the pressure equally important in the Haber and Contact processes?
IntermediateWhat does raising the temperature do to the yield and to the rate in the Haber process?
IntermediateFrom 3 mol of nitrogen the theoretical yield is 6 mol of ammonia, but 4.5 mol is obtained. What is the yield?
IntermediateIf 46 kJ is released per mole of ammonia, how much heat is released by 0.5 mol?
ChallengeWith a single pass conversion of 40 per cent, what is the overall conversion after four recycles?
ChallengeWhy is the atom economy of the Haber process 100 per cent?
ChallengeWhen 28 g of nitrogen reacts fully with 6 g of hydrogen, what mass of product should appear and which principle checks it?
Error redoA student says a high yield means a high profit. What does that leave out?

03　Answers and one-line notes

#	Answer	One-line note
1	No. It only shortens the time taken to reach equilibrium, and the position is unchanged	The forward and reverse reactions are speeded up equally, so the equilibrium constant and the yield stay the same.
2	No. The forward reaction is exothermic and a high temperature actually lowers the yield; 450 degrees C is a compromise between rate and yield	Treating an exothermic reaction as endothermic is a common slip, so always check the sign of dH before reasoning about temperature.
3	No. Pressure pays off clearly in the Haber process, while the Contact process works well at ordinary to low pressure	Look at the difference in gas moles across the equation and at how high the yield already is at ordinary pressure.
4	The yield falls and the rate rises	Heating shifts an exothermic equilibrium backwards yet gives the particles more energy so the reaction is faster; the two effects pull in opposite directions.
5	75.0 per cent	4.5 divided by 6 times 100 gives 75.0, and the shortfall of 1.5 mol is recycled.
6	23 kJ	46 times 0.5 is 23, and the heat released is proportional to the number of moles formed.
7	About 87.04 per cent	One minus 0.6 to the fourth power gives 0.8704, which is about 87.04 per cent.
8	Because every atom of the reactants ends up in ammonia with no by-product, so 34 g of reactants gives 34 g of ammonia	Atom economy looks only at the equation and not at the actual yield, so it stays at 100 per cent even when the yield is low.
9	34 g, checked by conservation of mass: 28 plus 6 equals 34	In a closed system the total mass does not change, which is the quickest check on any calculation of this kind.
10	Compression, heating, catalyst replacement and recycling all cost energy, so a higher yield can still lose money	Plant decisions are made on the whole economics rather than on one yield figure.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

Turn every wrong item today into one sentence: I thought this, but actually that.Tutor Registration →

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