Chemical Kinetics

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Chemical Kinetics — Key Facts Rate of reaction: change in concentration per unit time; for $aA + bB \rightarrow products$, rate $= -\frac{1}{a}\frac{d[A]}{dt} = -\frac{1}{b}\frac{d[B]}{dt} = +\frac{1}{c}\frac{d[C]}{dt}$ Rate law: rate $= k[A]^m[B]^n$ where $m, n$ are order with respect to each reactant (determined experimentally, NOT from stoichiometry) Rate constant $k$: temperature dependent, given by Arrhenius equation $k = Ae^{-E_a/RT}$ ⚡ Exam tip: Order is experimental; molecularity is theoretical. A reaction can be unimolecular but third-order overall.

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Chemical Kinetics — JAMB Chemistry Study Guide Zero order: $[A]_t = [A]0 - kt$; half-life $t{1/2} = [A]_0/2k$ (independent of initial concentration) First order: $\ln[A]_t = \ln[A]_0 - kt$ or $[A]_t = [A]0 e^{-kt}$; half-life $t{1/2} = \ln 2/k = 0.693/k$ (independent of initial concentration) Second order: $\frac{1}{[A]_t} = \frac{1}{[A]0} + kt$; half-life $t{1/2} = 1/(k[A]_0)$ (depends on initial concentration)

Factors affecting rate:

• Concentration: higher concentration → more collisions → faster rate
• Temperature: $k$ increases with $T$; roughly rate doubles for every 10°C rise (Arrhenius)
• Catalyst: lowers activation energy $E_a$, increases rate without being consumed
• Surface area: important for solid reactants; powdered = larger surface area = faster
• Light: some reactions (e.g., halogenation of alkanes) are photochemical

Activation energy $E_a$: minimum energy required for reaction to occur; higher $E_a$ = slower reaction. Arrhenius equation: $k = Ae^{-E_a/RT}$; taking logs: $\ln k = \ln A - \frac{E_a}{RT}$ ⚡ Exam tip: When temperature increases, $k$ increases and rate increases. The exponential dependence means small temperature changes cause large rate changes.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Chemical Kinetics — Comprehensive Chemistry Notes

Collision theory: For a reaction to occur:

1. Collision must happen between reactant molecules
2. Collision must have sufficient energy (≥ $E_a$)
3. Collision must have correct orientation (steric factor)

Rate $= PZ_{AB} e^{-E_a/RT}$ where $P$ = steric factor, $Z_{AB}$ = collision frequency.

Transition state theory: Activated complex (transition state): temporary high-energy intermediate formed when reactants pass through maximum on reaction coordinate diagram. For reaction $A + B \rightarrow [AB]^{\ddagger} \rightarrow products$: $\Delta G^{\ddagger} = -RT \ln K^{\ddagger}$ where $K^{\ddagger}$ relates to the rate constant.

Order determination methods:

1. Initial rates method: measure initial rate at different initial concentrations; keep other reactant constant.
2. Half-life method: measure $t_{1/2}$ at different $[A]0$; if $t{1/2}$ constant → zero order; if $t_{1/2}$ doubles when $[A]_0$ halves → first order.

Examples of reaction orders:

Reaction	Rate law	Order
$N_2O_5 \rightarrow N_2O_4 + \frac{1}{2}O_2$	rate $= k[N_2O_5]$	1st
$2NO_2 \rightarrow 2NO + O_2$	rate $= k[NO_2]^2$	2nd
$CH_3CHO \rightarrow CH_4 + CO$	rate $= k[CH_3CHO]^{3/2}$	3/2
$H_2 + I_2 \rightarrow 2HI$	rate $= k[H_2][I_2]$	2nd

Rate constant units: Units depend on overall order to give rate in mol/L/s.

Overall order	Units of k
Zero	mol L⁻¹ s⁻¹
First	s⁻¹
Second	L mol⁻¹ s⁻¹
Third	L² mol⁻² s⁻¹

JAMB exam patterns:

• 2023 JAMB: For reaction A → products, half-life is 10 min when [A]₀ = 0.1 M; what is half-life when [A]₀ = 0.4 M?
• 2022 JAMB: State the effect of increasing temperature on rate constant and explain using Arrhenius equation
• 2021 JAMB: For reaction 2A + B → products, rate = k[A]²[B]°; what is the order with respect to A, B, and overall?
• 2020 JAMB: Calculate activation energy given rate constants at two temperatures

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📊 JAMB Exam Essentials

Detail	Value
Questions	180 MCQs (UTME)
Subjects	4 subjects (language + 3 for course)
Time	2 hours
Marking	+1 per correct answer
Score	400 max (used for university admission)
Registration	January – February each year

🎯 High-Yield Topics for JAMB

• Use of English (Grammar + Comprehension) — 60 marks
• Biology for Science students — 40 marks
• Chemistry (Organic + Physical) — 40 marks
• Physics (Mechanics + Optics) — 35 marks
• Mathematics (Algebra + Geometry) — 40 marks

📝 Previous Year Question Patterns

• Q: “The process of photosynthesis requires…” [2024 Biology]
• Q: “The electronic configuration of Fe is…” [2024 Chemistry]
• Q: “Find the value of x if 2x + 5 = 15…” [2024 Mathematics]

💡 Pro Tips

• Use of English carries the most weight — master grammar rules and comprehension strategies
• JAMB syllabus is your Bible — questions come directly from it. Download and use it.
• Past questions are highly predictive — repeat patterns appear every year
• For Science students, Biology and Chemistry are high-scoring if you study NCERT-level content

🔗 Official Resources

• JAMB Official
• JAMB Syllabus

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