Topic 3 of 6 · Form 5
Equilibria and reaction kinetics
Dynamic equilibrium; Le Chatelier's principle; Kc and Kp expressions and calculations; only temperature changes K.
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Chemical equilibrium
Dynamic equilibrium; Le Chatelier's principle; Kc and Kp expressions and calculations; only temperature changes K.
Worked example: For H₂ + I₂ ⇌ 2HI at equilibrium: [H₂] = 0.10, [I₂] = 0.10, [HI] = 0.70 mol dm⁻³. Find Kc.
Kc = 0.70² ÷ (0.10 × 0.10) = 49
Acid–base equilibria
Brønsted–Lowry theory; pH = −log[H⁺]; Kw; Ka and pKa for weak acids; buffer solutions (pH = pKa + log([A⁻]/[HA])); titration curves and indicators; solubility product Ksp and the common ion effect.
Reaction kinetics
Rate equations, orders, rate constants and units; half-life for first-order reactions; rate-determining step and mechanisms; Boltzmann distribution; catalysis (homogeneous and heterogeneous; enzymes); the Arrhenius equation k = Ae^(−Ea/RT).
Worked example: A first-order reaction has k = 0.0231 min⁻¹. Find its half-life.
t½ = 0.693 ÷ 0.0231 = 30 min
Check yourself
- Find the pH of 0.050 mol dm⁻³ NaOH at 298 K.
- Write the Ksp expression for PbI₂.
- How does a catalyst affect the Boltzmann distribution analysis?
Show answers
- pOH = 1.30 → pH = 12.70
- Ksp = [Pb²⁺][I⁻]²
- It lowers the activation energy, so more particles have energy ≥ Ea.
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