FAD1018 Kinetic Chemistry — Part B Prediction & Breakdown

[!warning] This is a prediction based on leaks, past-year patterns, and lecture content. Not a confirmed exam paper.

1. What We Know

From Vick's Leak

B7: Kinetic Chemistry — Graph-based question.

  • Straight line with k as gradient and t as x-axis
  • Y-axis depends on reaction order:
    • Zero order: [A] vs t
    • First order: ln[A] vs t
    • Second order: 1/[A] vs t
  • No past-year reference listed for B7 (this may be a new question format)

From Past-Year Patterns

Kinetic chemistry has historically appeared in Section A (structured, ~5 marks). The 2025-2026 leak places it in Section B (long question, ~12-15 marks) — this is a shift in weight and suggests a much more involved question than before.

From Lecture Content (W16 — Kinetic Chemistry)

The lecture covers:

  1. Reaction rates & differential rate equations
  2. Rate laws & method of initial rates
  3. Integrated rate laws & graphical determination of order
  4. Half-life formulas (all three orders)
  5. Collision theory & energy profile diagrams
  6. Maxwell-Boltzmann distribution
  7. Arrhenius equation (calculations + graphical)
  8. Reaction mechanisms & rate-determining step
  9. Catalysis (homogeneous, heterogeneous)
  10. Enzyme kinetics (Michaelis-Menten)

2. The 15-Mark Puzzle — What Fits?

A 15-mark question in Part B typically has 4-6 sub-questions branching from a single stem. The stem (as per the leak) is a concentration-time graph from which students must determine the reaction order.

Let's map every possible sub-question to available marks:

Tier 1: Directly from the Graph (Locked In)

Sub-Q Task Marks Certainty
(a) Plot or interpret given [A]-time data, determine order by testing which linear plot works 4-5 ✅ Leak-confirmed
(b) Calculate k from gradient 2 ✅ Direct consequence of (a)
(c) Write the rate law (Rate = k[A]ⁿ) 1 ✅ Flows from (a)+(b)

Subtotal: 7-8 marks — these are basically guaranteed.

Tier 2: Very Likely Extensions

Sub-Q Task Marks Why It Fits
(d) Calculate half-life (t₁/₂) from k 2-3 Standard follow-up. Lecture spends significant time on half-life.
(e) Calculate [A] at a given time or time to reach a given [A] using integrated rate law 2-3 Every worked example in lecture has one of these.

Subtotal: 4-6 marks

Tier 3: Possible (Based on Available Marks)

These fit the remaining marks and are within the syllabus:

Sub-Q Task Marks Plausibility
(f) Explain what happens if temperature is increased (Maxwell-Boltzmann curve draw/explain) 2-3 🟡 Possible — MB curve is exam staple ("selalu keluar exam")
(g) Use Arrhenius two-point form to calculate Eₐ or k at another temperature 3-4 🟡 Possible — standard calculation question, fits B-section style
(h) Energy profile diagram — label Eₐ, ΔH, activated complex, determine exo/endo 2-3 🟡 Possible — "selalu keluar exam" per lecture. But feels more like A-section
(i) Draw/explain effect of catalyst on energy profile 2-3 🔴 Less likely — more suited to Section A
(j) Reaction mechanism — propose RDS, validate against experimental rate law 3-4 🔴 Less likely — this would be a separate question
(k) Collision theory — explain why certain conditions affect rate 2 🔴 Less likely — too short for B-section; more of an A-section definition

Your Guess vs This Breakdown

Your Prediction Marks Verdict
Graph (draw/interpret) ~5 ✅ Agreed. Leak confirms graph-based.
Explain graph ~2 ✅ Likely — explaining which plot is linear and why that determines order
Write rate law ~1 ✅ Flows naturally from steps above
Half-life ~3 ✅ Very likely follow-up
Arrhenius equation ~3 🟡 Possible but less directly connected to the graph stem

Missing from your list: Finding [A] at a given time (or time to reach a given [A]) using the integrated rate law — this is a very natural extension and shows up in every worked example in the lecture.

3. The Most Likely Question Structure

Based on the leaks + lecture focus + typical Part B format, here's my best guess for the question skeleton:

Stem

You are given concentration-time data for a reaction A → Products:

Time (min) 0 10 20 30 40 50 60
[A] (M) 1.00 0.75 0.56 0.42 0.32 0.24 0.18

(or similar data that clearly fits one order)

Sub-Questions (Total: 15 marks)

(a) Plot [A] vs t, ln[A] vs t, and 1/[A] vs t. Determine the order of reaction. Explain your reasoning. [5 marks]

(b) Calculate the rate constant, k, including its units. [2 marks]

(c) Write the rate law for this reaction. [1 mark]

(d) Calculate the half-life of this reaction. [3 marks]

(e) Determine the concentration of A after 90 minutes. [2 marks]

(f) If the temperature is increased by 20°C, explain how the rate constant k would change. Use the Arrhenius equation in your explanation. [2 marks]

Why This Structure Works

Question Skill tested Links to lecture
(a) Graphical determination of order W16 p.34-48 — integrated rate law linear plots
(b) k from gradient W16 p.34-48 — slope = ±k
(c) Rate law expression W16 p.20-25 — rate law basics
(d) Half-life calculation W16 p.49-58 — t₁/₂ formulas
(e) Integrated rate law application W16 worked examples — finding [A] at time t
(f) Arrhenius + MB curve W16 p.83-97 — Arrhenius, temperature effect

4. Less Likely But Not Impossible Additions

Boltzmann Curve Drawing

Why it could fit: The lecturer explicitly says "Selalu keluar exam" for MB distribution. A 2-mark sub-question asking to "Draw the Maxwell-Boltzmann distribution curve at two temperatures and explain the effect on reaction rate" is very plausible.

Why it doesn't fit perfectly: The stem is a concentration-time graph, and MB is a separate concept. It would require a new context, which is unusual for a B-question that typically builds on one stem.

Verdict: 🟡 Possible as part (f) or (g) within a 15-mark limit.

Arrhenius Numerical Calculation

Why it could fit: Two-point Arrhenius is a standard calculation. The lecture has multiple worked examples (p. 98-100).

Why it doesn't fit perfectly: Same issue — requires introducing a second temperature or Eₐ value not present in the graph stem.

Verdict: 🟡 Possible if the question provides data in two parts: Part I (graph-based, ~10 marks) + Part II (Arrhenius, ~5 marks).

Energy Profile Diagram

Why it could fit: "Selalu keluar exam" from the lecture notes.

Why it might not: More likely in Section A (Thermochemistry or basic kinetics) than Section B. Would feel disconnected from the graph stem.

Verdict: 🔴 More likely in Section A (A7 or A6).

Reaction Mechanisms

Why it could fit: Part 2 of W16 covers mechanisms, RDS, molecularity.

Why it might not: This is a substantial topic — would need its own context. Usually paired with a specific experimental rate law.

Verdict: 🔴 Would be a separate B-question, not tied to the graph stem.

5. What to Practise

Must-Do (High Probability)

Skill How to Practise Source
Plot [A], ln[A], 1/[A] vs t from raw data and decide order Take any concentration-time dataset and test all three plots W16 p.34-48, Tutorial 1
Calculate k from a linear plot's gradient Given a linear plot, find slope → k W16 worked examples
Write rate law with correct k units Rate = k[A]ⁿ, determine unit from overall order W16 p.26-30
Half-life calculation Use correct t₁/₂ formula for the determined order W16 p.49-58, Tutorial 1
Find [A] at time t (or t for given [A]) Plug into integrated rate law W16 worked examples

Should-Do (Medium Probability)

Skill How to Practise Source
Explain why a particular plot is linear for a given order Understand that integrated form is y = mx + c W16 p.34-48
Maxwell-Boltzmann curve: draw two temperatures, label Eₐ, explain Practise drawing T₁ vs T₂, mark area above Eₐ W16 p.85-88
Two-point Arrhenius calculation ln(k₂/k₁) = (Eₐ/R)(1/T₁ − 1/T₂) W16 p.91-100, Tutorial 2
Energy profile diagram: label Eₐ, ΔH, activated complex, exo/endo Practise from W16 p.68-70 W16 p.68-70

Could-Do (Lower Probability)

Skill How to Practise Source
Catalyst effect on energy profile Draw two curves, label lower Eₐ path W16 p.80-82
Collision theory explanation (energy + orientation) Understand requirements for effective collision W16 p.61-63
Reaction mechanism → validate against rate law Given steps + experimental rate law, check consistency W16 Part 2

6. Key Formulas to Memorise Cold

Integrated Rate Laws (Linear Forms)

Order Equation Plot (y vs x) Slope
0 [A]ₜ = −kt + [A]₀ [A] vs t −k
1 ln[A]ₜ = −kt + ln[A]₀ ln[A] vs t −k
2 1/[A]ₜ = kt + 1/[A]₀ 1/[A] vs t +k

The key insight: Only one of these three plots will be linear for a given dataset. That tells you the order.

Half-Life Formulas

Order t₁/₂ Behaviour
0 [A]₀ / 2k Decreases (masa ↓)
1 0.693 / k Constant (masa sama)
2 1 / k[A]₀ Increases (masa ↑)

Arrhenius

$$k = Ae^{-E_a/RT}$$ $$\ln k = -\frac{E_a}{R}\left(\frac{1}{T}\right) + \ln A$$ $$\ln\frac{k_2}{k_1} = \frac{E_a}{R}\left(\frac{1}{T_1} - \frac{1}{T_2}\right)$$

7. Common Traps

Trap Detail
k units wrong k unit depends on overall order: M^(1−n)s⁻¹. Don't just write "s⁻¹"
Rate law vs stoichiometry Rate law exponents ≠ stoichiometric coefficients ("takde kaitan")
Slope sign for second order 1/[A] vs t has positive slope (+k). The other two are negative.
Half-life formula mix-up First-order: no [A]₀ in formula. Second-order: [A]₀ in denominator. Zero-order: [A]₀ in numerator.
Arrhenius units Eₐ in kJ/mol → convert to J/mol before plugging into R = 8.314 J/mol·K
Temperature in Kelvin Always convert °C to K: T(K) = T(°C) + 273
Explaining linearity The question may ask why a particular plot is linear — answer: because the integrated rate law has the form y = mx + c

8. Quick Reference — Mark Allocation by Topic

Topic Likely Marks Format
Graph interpretation / order determination 4-5 Plot analysis + reasoning
Rate constant calculation 2 From gradient
Rate law 1 Written expression
Half-life 2-3 Calculation
Integrated rate law application 2 Find [A] or t
Arrhenius / temperature effect 2-3 Calculation or explanation
MB distribution / catalyst 2-3 Diagram + explanation
Total ~15 —

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