Equilibrium and Ionic Equilibrium

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Equilibrium and Ionic Equilibrium — Key Facts Law of mass action: for $aA + bB \rightleftharpoons cC + dD$, $K_{eq} = \frac{[C]^c[D]^d}{[A]^a[B]^b}$ (at equilibrium) $K_p = K_c(RT)^{\Delta n}$ where $\Delta n = (c+d) - (a+b)$ Le Chatelier’s principle: system at equilibrium adjusts to counteract applied change ⚡ Exam tip: Increasing temperature shifts equilibrium towards endothermic direction; decreasing temperature shifts towards exothermic direction

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Equilibrium and Ionic Equilibrium — JAMB Chemistry Study Guide Homogeneous equilibrium: all species in same phase (gaseous or aqueous) Example: $N_2 + 3H_2 \rightleftharpoons 2NH_3$; $K_c = \frac{[NH_3]^2}{[N_2][H_2]^3}$

Heterogeneous equilibrium: species in different phases Example: $CaCO_3(s) \rightleftharpoons CaO(s) + CO_2(g)$; $K_p = P_{CO_2}$ (solids omitted from expression)

Ionic equilibrium — weak acids and bases: For weak acid HA: $K_a = \frac{[H^+][A^-]}{[HA]}$; $pK_a = -\log K_a$ For weak base B: $K_b = \frac{[BH^+][OH^-]}{[B]}$; $pK_b = -\log K_b$ $pH = -\log[H^+]$; $pOH = -\log[OH^-]$; $pH + pOH = 14$ at 25°C

Buffer solutions: resist pH change on addition of small amounts of acid/base Henderson-Hasselbalch: $pH = pK_a + \log\frac{[A^-]}{[HA]}$ for acid buffer Common buffer: acetic acid + sodium acetate ($CH_3COOH/CH_3COONa$)

Solubility product: $K_{sp} = [A^+]^m[B^-]^n$ for $A_mB_n(s) \rightleftharpoons mA^+ + nB^-$ ⚡ Exam tip: If ionic product > $K_{sp}$, precipitation occurs; if < $K_{sp}$, no precipitate.

Common student mistakes: forgetting that pure solids and liquids don’t appear in $K$ expression; confusing $K_a$ with $K_b$ for conjugate pairs ($K_a \times K_b = K_w$); not converting concentrations properly.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Equilibrium and Ionic Equilibrium — Comprehensive Chemistry Notes

Relationship between K_a and K_b for conjugate pairs: For acid HA and its conjugate base A⁻: $HA \rightleftharpoons H^+ + A^-$ with $K_a = \frac{[H^+][A^-]}{[HA]}$ $A^- + H_2O \rightleftharpoons HA + OH^-$ with $K_b = \frac{[HA][OH^-]}{[A^-]}$ Since $K_w = [H^+][OH^-] = 10^{-14}$ at 25°C: $$K_a \times K_b = \frac{[H^+][A^-]}{[HA]} \times \frac{[HA][OH^-]}{[A^-]} = [H^+][OH^-] = K_w$$ Therefore: $pK_a + pK_b = pK_w = 14$

Salt hydrolysis: Salt of strong acid + weak base (e.g., $NH_4Cl$): solution is acidic Salt of weak acid + strong base (e.g., $NaCH_3COO$): solution is basic Salt of weak acid + weak base: $pH = \frac{1}{2}(pK_a + pK_w - pK_b)$

Buffer capacity: Maximum amount of acid or base that can be added without pH changing significantly. Depends on concentration of buffer components.

Common ion effect: Adding a salt containing one ion common to the equilibrium shifts equilibrium. Example: adding $NaCl$ to equilibrium $AgCl(s) \rightleftharpoons Ag^+ + Cl^-$ suppresses $AgCl$ dissolution (lowers $[Ag^+]$).

K_p and K_c relationship: For ideal gases, $PV = nRT$, so $[A] = \frac{n}{V} = \frac{P}{RT}$ For $aA + bB \rightleftharpoons cC + dD$: $$K_p = \frac{P_C^c P_D^d}{P_A^a P_B^b} = \frac{([C]RT)^c([D]RT)^d}{([A]RT)^a([B]RT)^b} = K_c(RT)^{(c+d)-(a+b)}$$ Therefore: $K_p = K_c(RT)^{\Delta n}$

JAMB exam patterns:

• 2023 JAMB: For reaction $PCl_5 \rightleftharpoons PCl_3 + Cl_2$, K_c = 0.020 at 250°C; initially 0.10 mol PCl_5 in 1 L; find equilibrium concentrations
• 2022 JAMB: State and explain Le Chatelier’s principle for the effect of adding a catalyst on equilibrium position
• 2021 JAMB: Calculate pH of 0.1 M acetic acid ($K_a = 1.8 \times 10^{-5}$)
• 2020 JAMB: Will precipitation occur when equal volumes of $0.001 M$ $AgNO_3$ and $0.001 M$ $NaCl$ are mixed? ($K_{sp}$ of $AgCl = 1.8 \times 10^{-10}$)

Important values:

Substance	K_a (at 25°C)
HCl (strong)	~10⁷
H₂SO₄ (1st proton)	very large
CH₃COOH	$1.8 \times 10^{-5}$
H₂CO₃	$4.3 \times 10^{-7}$
H₃BO₃	$5.8 \times 10^{-10}$

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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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