Chemical Equilibrium

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Chemical Equilibrium — Key Facts Dynamic equilibrium: forward and reverse reactions occur at equal rates; concentrations remain constant Law of mass action: for $aA + bB \rightleftharpoons cC + dD$, $K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$ at equilibrium Homogeneous: all species in same phase; Heterogeneous: species in different phases (omit solids/liquids from $K$) Le Chatelier’s principle: system at equilibrium shifts to counteract any applied change ⚡ Exam tip: Adding a catalyst increases rate of both forward and reverse equally; it does NOT change equilibrium position or $K$

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Chemical Equilibrium — JAMB Chemistry Study Guide

Types of equilibrium constant: $K_c$: concentrations in mol/L; $K_p$: partial pressures (for gaseous reactions); $K_{sp}$: solubility product $K_c = K_p(RT)^{-\Delta n}$ where $\Delta n = n_{gaseous products} - n_{gaseous reactants}$

Physical equilibrium examples:

• Water evaporation: $H_2O(l) \rightleftharpoons H_2O(g)$; $K_p = P_{H_2O}$ (vapour pressure)
• Ice-water: $H_2O(s) \rightleftharpoons H_2O(l)$
• Dissolution of gases: $CO_2(g) \rightleftharpoons CO_2(aq)$

Le Chatelier’s effects:

Change	Effect on equilibrium
Increase $[A]$	Shift away from A
Decrease $[A]$	Shift toward A
Increase pressure	Shift toward fewer gas moles
Decrease pressure	Shift toward more gas moles
Increase temperature (exothermic)	Shift left
Increase temperature (endothermic)	Shift right
Add catalyst	No shift

Heterogeneous equilibrium example: $CaCO_3(s) \rightleftharpoons CaO(s) + CO_2(g)$ $K_p = P_{CO_2}$ (solids don’t appear) This is why $CaCO_3$ decomposition continues only if $P_{CO_2}$ is kept low (limestone calcination in kilns).

Common student mistakes: forgetting that pure solids and liquids are omitted from $K$ expressions; confusing Le Chatelier’s for concentration vs partial pressure changes; thinking $K$ changes with concentration (it doesn’t — only with temperature).

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Chemical Equilibrium — Comprehensive Chemistry Notes

Relationship between K and reaction quotient Q: $Q = \frac{[C]^c[D]^d}{[A]^a[B]^b}$ (same formula as $K$ but concentrations are not at equilibrium)

• If $Q < K$: reaction proceeds forward (products need to increase)
• If $Q > K$: reaction proceeds reverse (reactants need to increase)
• If $Q = K$: at equilibrium

Temperature dependence of K: $\ln K = -\frac{\Delta H°}{RT} + \frac{\Delta S°}{R}$ Or: $\ln\frac{K_2}{K_1} = -\frac{\Delta H°}{R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right)$ For exothermic reactions ($\Delta H° < 0$): as $T$ increases, $K$ decreases. For endothermic reactions ($\Delta H° > 0$): as $T$ increases, $K$ increases.

Very large or very small K:

• $K >> 1$: products heavily favoured; reaction goes essentially to completion
• $K << 1$: reactants heavily favoured; reverse reaction predominates
• $K = 1$: significant amounts of both reactants and products at equilibrium

Equilibrium calculations: For $aA \rightleftharpoons bB$: Let initial: $[A]_0 = a_0$, $[B]_0 = b_0$ Change: $[A]$ decreases by $x$, $[B]$ increases by $(b/a)x$ At equilibrium: $[A] = a_0 - x$, $[B] = b_0 + (b/a)x$ $K = \frac{[B]^b}{[A]^a} = \frac{(b_0 + (b/a)x)^b}{(a_0 - x)^a}$

The Haber process (industrial example): $N_2 + 3H_2 \rightleftharpoons 2NH_3$; $\Delta H = -92.4$ kJ/mol (exothermic) Low temperature favours products BUT slows reaction rate (compromise at ~400-500°C with catalyst). High pressure favours products (4 moles gas → 2 moles gas) — typically 150-300 atm. Iron catalyst speeds up reaction without affecting equilibrium position.

JAMB exam patterns:

• 2023 JAMB: For reaction $2SO_2 + O_2 \rightleftharpoons 2SO_3$, K_c = 4; if initial [SO₂] = 2 M and [O₂] = 1 M, find equilibrium [SO₃]
• 2022 JAMB: State Le Chatelier’s principle and predict effect of adding a catalyst on equilibrium constant
• 2021 JAMB: For $N_2 + 3H_2 \rightleftharpoons 2NH_3$, explain why low temperature favours ammonia formation despite slow rate
• 2020 JAMB: Why does increasing pressure shift equilibrium toward fewer gas molecules?

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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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