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sub90 ESATsub90 ESAT SyllabusARCH-C-04
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UAT-UK SPEC: C4MODULE: CHEMISTRYTOPIC ID: ARCH-C-04

Molar Gas Volume (24 dm³ at rtp), Ideal Gas Scaling, Percentage Yield & Atom Economy

Master Molar Gas Volume (24 dm³ at rtp), Ideal Gas Scaling, Percentage Yield & Atom Economy on the ESAT Chemistry paper. Traditional classroom derivations waste valuable seconds. Using the 2-step Sub-90 invariant elimination method compresses solve time to 40s, saving +110s per question.

Standard Classroom Time
150s
Textbook multi-line derivations bleed exam clock
Sub-90 Target Pace
40s
Comfortably below the 88.8s per-question limit
Time Saved for Review
+110s
Banks clock buffer across 27 questions

2-Step Sub-90 Shortcut Formula

How to eliminate intermediate algebra and solve under 45 seconds.

Launch Interactive Lesson
STEP 1 • SETUP INVARIANT (LINE 1)10–15s
Line 1 (2424 Cancellation): V(cm3)=mAr×24,000=0.6024×24,000V(\text{cm}^3) = \frac{m}{A_r} \times 24,000 = \frac{0.60}{24} \times 24,000.

Establish the structural invariant and eliminate impossible options immediately.

STEP 2 • FAST SOLVE (LINE 2)15–25s
Line 2 (Cancel 2424): 0.60×1000=600 cm30.60 \times 1000 = 600\text{ cm}^3 (20s).

Evaluate the simplified expression using integer factoring or unit elimination.

Distractor Trap Forensics

The predictable cognitive traps engineered by examiners into the wrong options.

TRAP #1unit_or_prefix_mismatch

Dividing cm³ by 24 instead of 24,000 when converting gas volume at rtp to moles

Mixing cm³ and dm³ without applying 1 dm³ = 1000 cm³.

Sub-90 Fix: Test invariants before expanding equations.
TRAP #2factor_of_two_or_stoichiometry_trap

Using atomic mass instead of diatomic Mᵣ (e.g. 14 instead of 28 for N₂, or 35.5 instead of 71 for Cl₂) when converting gas volume to mass

Forgetting that common elemental gases (H2, N2, O2, F2, Cl2) are diatomic.

Sub-90 Fix: Test invariants before expanding equations.
TRAP #3subsystem_isolation_trap

Swapping percentage yield (actual / theoretical * 100%) with atom economy (Mᵣ of desired product / sum of Mᵣ of all products * 100%)

Confusing experimental reaction efficiency (% yield) with stoichiometric formula utilization (atom economy).

Sub-90 Fix: Test invariants before expanding equations.

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Full Lesson All 15 Questions (ARCH-C-04)
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ARCH-C-04: Molar Gas Volume (24 dm³ at rtp), Ideal Gas Scaling, Percentage Yield & Atom Economy (Sample)Chemistry
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SUB-90 ZONE (<35S)
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Question 1 of 1ARCH-C-04 (6-Card Lesson)Format: Standard 5-Option
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