A Secondary 4 G3 Chemistry tutor can prepare an industrial-conditions question by supplying clear data about product yield, reaction rate and operating constraints. The student should use those data to justify a choice, identify the compromise and explain why the highest value in one column may not satisfy the whole brief.
For Hougang students, a data-based ammonia question is useful when it asks for more than a remembered temperature or pressure. A carefully written table lets the tutor see whether the student compares like conditions, applies every requirement and distinguishes the amount available at equilibrium from how quickly a reaction approaches it.
This guide uses an original fictional decision table for the manufacture of ammonia. It supports interpretation of data for reversible reactions in the 2027 separate G3 Chemistry syllabus K324, which does not require knowledge of Le Chatelier’s principle. The numbers are teaching illustrations and are not plant specifications, actual operating costs or recommended industrial settings.
EDUKATESG · HOUGANG CHEMISTRY · TUTOR PREPARATION
Find the next teaching move
Choose the closest preparation route, or follow the complete guide.
ROUTE 2 · CHAPTERS 3–4
Follow the worked reasoning
Connect each conclusion to the supplied information.
Full chapter index · Tutor checklist · Hougang Chemistry learning routes
Full chapter index
Chapters 1–3: purpose, evidence and first example
Chapters 4–7: comparisons, interpretation and limits
Chapters 8–10: feedback, transfer and continuation
CHAPTER 1 OF 10 · Define the teaching decision
1. Define the decision and the limits of the evidence
Write the task as a decision among stated candidate conditions. The student must select a candidate that satisfies the supplied yield, rate and cost requirements and support the choice numerically. This makes the intended reasoning concrete and keeps the answer grounded in the stimulus.
State that the task compares the listed candidates only. A best listed option is not necessarily the globally optimal industrial condition. A real engineering design would require more information about equipment, energy, safety, separation, catalyst life and market conditions.
Separate three quantities before giving the table: equilibrium yield, a relative initial-rate index and an operating-cost index. They describe different features of a process. A student who treats all three as versions of efficiency may choose the wrong condition for a plausible-sounding reason.
Ask what information the question provides and what it asks the student to infer. The table supplies trends and numerical values. The student uses those data to justify a feasible choice; advanced equilibrium calculations are not a hidden prerequisite.
Prepare a short answer format with candidate, evidence and trade-off. It should give enough space for the reasoning without turning the task into a long report. The tutor can then check whether every claimed advantage refers to a specific column or comparison.
CHAPTER 2 OF 10 · Define the teaching decision
2. Supply the reversible reaction and define yield
Give N₂(g) + 3H₂(g) ⇌ 2NH₃(g), and state that the forward reaction is exothermic. The reversible arrow indicates that ammonia can form and also react in the reverse direction under appropriate conditions.
For this exercise, define equilibrium yield as the ammonia amount at equilibrium expressed as a percentage of the theoretical ammonia amount from the stated stoichiometric feed. Use the same feed basis and no initial ammonia for every listed candidate.
Supply a reference feed of 100 mol N₂ and 300 mol H₂. Complete conversion in the forward direction would form 200 mol NH₃. A 32% equilibrium yield on this basis therefore corresponds to 0.32 × 200 = 64 mol NH₃.
The yield percentage is not automatically the percentage of ammonia molecules in the final gas mixture. Reaction changes the total gas amount, and unreacted nitrogen and hydrogen remain. Keep the yield definition visible so that the student does not substitute a different denominator.
Use the balanced equation to check the basis before applying percentages. The values 100, 300 and 200 are paper quantities chosen for clear arithmetic. They do not specify reactor charge amounts or a practical operating procedure.
CHAPTER 3 OF 10 · Follow the worked reasoning
3. Define the rate and cost columns separately
Define the relative initial-rate index as a supplied comparison from the same standardised starting-composition protocol, using the stated temperature and pressure for each candidate. It has no physical unit in this exercise and serves only to compare the listed values.
Define the operating-cost index as a supplied fictional relative score with lower values representing lower cost for the purposes of the task. Do not convert the scores into dollars or imply that their numerical differences are real industrial expense estimates.
An initial-rate index is not an equilibrium yield. A reaction can begin faster under one condition while giving a lower equilibrium yield in the supplied dataset. The student needs both columns to assess the specific brief.
Likewise, dividing yield by rate index does not produce a validated production time. The rate changes as composition changes, and the index is not a time or a constant throughput. Any time-to-target calculation would require appropriate additional data.
State the screening requirements: equilibrium yield at least 30%, initial-rate index at least 50 and operating-cost index no more than 5.0. The words at least and no more than include equality, so a value exactly on a threshold passes that requirement.
CHAPTER 4 OF 10 · Follow the worked reasoning
4. Read temperature effects through a controlled comparison
At a fixed pressure of 150 bar, give candidate A at 350°C with yield 40%, rate index 20 and cost index 4.0; candidate C at 400°C with yield 32%, rate index 60 and cost index 4.5; and candidate B at 450°C with yield 25%, rate index 80 and cost index 5.0.
Every pressure in the table is expressed in bar. The numerical values are fictional comparison data for the paper task. They provide a consistent pressure scale without establishing actual performance or recommended operating conditions for an industrial plant.
Across A, C and B, increasing temperature is associated with a higher initial-rate index and a lower equilibrium yield. This conclusion uses the listed values at the same pressure and feed basis. The direction can be read directly from the table.
Ask the student to quote two comparisons rather than write higher temperature is better. From A to C the rate index rises from 20 to 60 while yield falls from 40% to 32%. Which change is beneficial depends on the requirement being considered.
Keep the word equilibrium attached to the yield column. The supplied trend does not mean that every higher-temperature sample contains less ammonia at every early time. A comparison of time-specific product amounts would need the relevant time data.
CHAPTER 5 OF 10 · Compare and explain
5. Apply all three requirements to the candidate table
Add candidate D at 400°C and 100 bar with yield 24%, rate index 45 and cost index 3.5. Add candidate E at 400°C and 200 bar with yield 38%, rate index 70 and cost index 7.0. Use the same feed basis and definitions.
Candidate A passes yield and cost but fails the rate requirement because 20 is below 50. Candidate B passes rate and cost but fails yield because 25% is below 30%. A high value in one column does not compensate for failing a required threshold.
Candidate D is inexpensive in the supplied comparison but fails both yield and rate. Candidate E passes yield and rate but fails cost because 7.0 exceeds 5.0. Candidate C meets all three: 32% yield, rate index 60 and cost index 4.5.
Thus C is the only listed candidate satisfying the screening brief. The justification should name all three passing values. The student does not need to guess actual industrial practice or introduce an unstated formula to reach this conclusion.
The table below is the complete original stimulus. Its purpose is to make the trade-offs inspectable. The numbers are not empirical equilibrium constants, plant measurements or a claim about the precise conditions used by any manufacturer.
| Candidate | Temperature / °C | Pressure / bar | Equilibrium yield / % | Initial-rate index | Cost index |
|---|---|---|---|---|---|
| A | 350 | 150 | 40 | 20 | 4.0 |
| B | 450 | 150 | 25 | 80 | 5.0 |
| C | 400 | 150 | 32 | 60 | 4.5 |
| D | 400 | 100 | 24 | 45 | 3.5 |
| E | 400 | 200 | 38 | 70 | 7.0 |
CHAPTER 6 OF 10 · Compare and explain
6. Compare pressure without changing temperature at the same time
Use D, C and E for a pressure comparison because all three are at 400°C. In the supplied dataset, increasing pressure from 100 to 150 to 200 bar accompanies yields of 24%, 32% and 38%, with rate indices of 45, 60 and 70.
The cost index also rises from 3.5 to 4.5 to 7.0. Under the stated ceiling of 5.0, the highest-pressure listed option is infeasible even though its yield and rate exceed C’s values. The conclusion follows the complete decision brief.
Ask why comparing A with E cannot isolate the pressure effect. Both temperature and pressure change between those candidates. The two-point comparison may describe a combined outcome, but it cannot attribute the difference uniquely to pressure.
If a pupil has learned a qualitative equilibrium explanation, connect it carefully to the reaction and the supplied trends. For this G3 task, however, the student can justify the selection from the data without recalling Le Chatelier’s principle.
A useful tutor check asks the student to mark the rows that form a controlled comparison before writing a trend. This small preparation step separates an evidence-selection difficulty from an incorrect understanding of the numerical values.
CHAPTER 7 OF 10 · Repair and transfer
7. Distinguish equilibrium, rate and catalyst effects
Explain equilibrium qualitatively as a dynamic condition in which forward and reverse reactions continue at equal rates in a closed system under unchanged conditions. The amounts remain constant overall; the reactions have not stopped.
Equal forward and reverse rates do not require equal amounts of nitrogen, hydrogen and ammonia. The composition depends on the system and conditions. The phrase equal rates should not become a statement that all substances have equal concentrations.
For a supplied catalyst comparison, state that an appropriate catalyst increases the rates of forward and reverse reaction and allows equilibrium to be reached sooner. At unchanged conditions it does not change the equilibrium composition.
Do not add catalyst benefits to the numerical table without specifying which rows use which catalyst conditions. A fair temperature or pressure comparison needs those other relevant features kept comparable or explicitly accounted for.
If the question asks for product after a fixed short time, a catalyst can affect that time-specific amount because the system may be closer to equilibrium. If it asks for equilibrium yield, keep the distinction clear. The question wording determines which quantity is relevant.
CHAPTER 8 OF 10 · Repair and transfer
8. Prepare feedback for predictable wrong choices
If the student selects A because 40% is the highest yield, ask for the rate threshold and A’s rate index. The yield observation is correct; the missing step is applying the complete brief. Marking every part wrong would hide that useful distinction.
If E is selected because pressure gives better results, ask the student to check its cost against the ceiling. The explanation needs a feasible decision, not only a trend. Use the actual values 7.0 and 5.0 to make the failed condition visible.
If B is selected because its rate index is 80, ask whether the yield requirement is also satisfied. Then compare B’s 25% with the required 30%. This targets the difference between faster reaction and sufficient equilibrium yield.
If the student compares A and E to prove a pressure effect, ask which other variable changes. Return to D, C and E for the fixed-temperature comparison. The repair is choosing evidence that supports the claimed cause.
If the student says equilibrium means the reaction has finished, ask how the forward and reverse rates are described in the supplied account. Then distinguish unchanged macroscopic amounts from ongoing particle-level reactions. Keep this explanation proportionate to the student’s taught level.
CHAPTER 9 OF 10 · Plan the next lesson
9. Check the yield basis and a changed decision brief
Return to candidate C’s 32% yield on the supplied feed. It forms 64 mol NH₃, consuming 32 mol N₂ and 96 mol H₂. The remaining amounts are 68 mol N₂ and 204 mol H₂ under the stated reaction model.
The total gas amount is 68 + 204 + 64 = 336 mol, so the ammonia mole fraction is 64/336, approximately 0.190 or 19.0%. This supplied-data extension shows why 32% yield is different from 32% ammonia in the gas mixture.
Give a changed screening brief: yield at least 35%, rate index at least 50 and cost index no more than 8.0. Candidate E now passes with 38%, 70 and 7.0. C fails the raised yield requirement, while A still fails rate.
The best listed choice changes because the requirements change. Ask the student to identify the altered thresholds and explain their effect. This checks independent decision-making rather than memorisation of C as the permanently correct condition.
For a parent update, describe whether the student can apply several constraints and select a fair comparison. If the percentage basis still needs support, identify that specific next step. A correct letter choice alone does not reveal whether the full reasoning is independent.
CHAPTER 10 OF 10 · Plan the next lesson
10. Audit the task and plan the next teaching move
Check the reaction equation, feed basis, equilibrium-yield definition, rate-index protocol and cost threshold. Recalculate every pass or fail decision and any percentage extension. Ensure the student copy contains the definitions used in the key.
Verify that claims about temperature use equal-pressure rows and claims about pressure use equal-temperature rows. Do not allow a key to infer a single-variable effect from a comparison in which several conditions change.
Keep industrial context truthful and proportionate. Separation of ammonia and recycling of unreacted gases can improve overall use of feed, but a single-pass equilibrium yield does not specify an entire plant’s total recovery or economic performance.
Choose repair when the student reads one column only, stabilise with a changed threshold and extend to a taught rate–time graph or a fuller process description when the basic decision is secure. Add complexity only when it tests a new reasoning step.
Retain the original choice, the corrected constraint check and the fresh-brief answer. Together they show whether the student can turn supplied reaction data into a justified decision. That evidence gives the following lesson a clearer purpose than another list of industrial conditions to memorise.
Contents · Previous chapter · Continue to the Chemistry library
Frequently asked questions
Which candidate meets the original brief?
C meets all three requirements: 32% equilibrium yield, rate index 60 and cost index 4.5. Every other listed candidate fails at least one threshold.
Why not choose the highest yield?
The task also requires sufficient rate and acceptable cost. Candidate A has the highest yield but its rate index of 20 falls below the required 50.
How do I compare pressure fairly?
Use D, C and E, which share the same temperature. Comparing rows with both different temperature and different pressure does not isolate pressure’s effect.
Does a catalyst raise the equilibrium yield?
At unchanged conditions an appropriate catalyst helps equilibrium be reached sooner without changing the equilibrium composition. A fixed-time product amount is a different quantity.
Is 32% yield the same as 32% ammonia in the gas mixture?
No. Yield uses the stated theoretical-product basis. In the worked feed example, 64 mol ammonia out of 336 mol total gas gives about 19.0% by mole.
Must students use Le Chatelier’s principle here?
The 2027 separate G3 syllabus supports interpretation of supplied reversible-reaction data without requiring that principle. Match additional explanations to the student’s taught course.
Tutor preparation checklist
| Check | Before the lesson |
|---|---|
| Brief | State every threshold and whether boundary values pass. |
| Definitions | Define yield basis, rate comparison and cost index. |
| Comparison | Use rows that hold other relevant variables fixed. |
| Decision | Check every candidate against every requirement. |
| Transfer | Change the brief and verify that the reasoning adapts. |
Continue with connected teaching guides
- Secondary 3 SEC G3 Chemistry Tutor | Preparing a Salt-Preparation Task That Matches the Reactants
- Secondary 4 SEC G3 Chemistry Tutor | Preparing an Electrolysis Question That Names the Electrolyte and Electrodes
- Hougang Chemistry Tuition and Tutor Library | Secondary 1–4 and JC Learning Routes
For a discussion about support, bring the student’s current Science or Chemistry course details, examination year and a recent piece of schoolwork showing the difficulty. Confirm current subject provision, grouping and teaching location directly with the provider. This guide describes preparation practice and does not establish class availability.
Sources and scope
SEAB: 2027 SEC G3 Chemistry syllabus, K324.
The worked examples, fictional datasets and tutor planning tools are original teaching illustrations. Use the applicable official course and examination-year documents to establish assessed scope and permitted resources. Optional supplied-data extensions are identified in the teaching discussion. Paper-based examples do not replace supervised practical instruction or constitute evidence of student outcomes.