Chemistry

Le Chatelier's Principle: when a system at dynamic equilibrium is subjected to a change, the equilibrium will shift to oppose that change. Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = −92 kJ mol⁻¹ • Increase pressure → equilibrium shifts right (fewer moles of gas) ✓ • Decrease temperature → shifts right (exothermic direction) ✓ but slow rate • Compromise: 450°C, 200 atm, iron catalyst — balances rate and yield

In terms of electrons: • Oxidation = Loss of electrons • Reduction = Gain of electrons (OIL RIG: Oxidation Is Loss, Reduction Is Gain) In terms of oxidation state: • Oxidation = increase in oxidation state • Reduction = decrease in oxidation state The oxidising agent is reduced (gains electrons). The reducing agent is oxidised (loses electrons).

Conditions: UV light (or high temperature) Mechanism (3 stages): 1. Initiation: Cl₂ → 2Cl• (UV light breaks the Cl−Cl bond homolytically) 2. Propagation (repeating): Cl• + CH₄ → HCl + CH₃• CH₃• + Cl₂ → CH₃Cl + Cl• 3. Termination: two radicals combine: Cl• + Cl• → Cl₂ CH₃• + Cl• → CH₃Cl

ΔG = ΔH − TΔS A reaction is spontaneous when ΔG < 0. | ΔH | ΔS | Spontaneous? | |−|+| Always (at all T) | |+|−| Never | |−|−| At low T only | |+|+| At high T only | Note: spontaneous ≠ fast. ΔG tells you thermodynamic feasibility, not rate.