The complete lecture — equilibrium comes alive in the live panel as you read. Scroll down; the animation keeps pace, and you can shift the Haber-process equilibrium yourself.
1 — Reversible & irreversible reactions
- Reversible reaction — proceeds in both directions; shown with ⇌, e.g. N₂ + 3H₂ ⇌ 2NH₃.
2 — Dynamic equilibrium
- Equilibrium — forward rate = reverse rate; concentrations stay constant. It is dynamic — both reactions continue.
3 — Characteristics of equilibrium
- Closed system; dynamic; constant concentrations.
- Reached from either side; a catalyst changes only the speed.
4 — Law of mass action & Kc
aA + bB ⇌ cC + dDKc = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ
5 — Kp and its relation to Kc
LinkKp = Kc (RT)^Δn (Δn = gas moles products − reactants)
6 — The significance of K
| K | Means |
|---|
| ≫ 1 | products favoured |
| ≈ 1 | both present |
| ≪ 1 | reactants favoured |
7 — Le Chatelier's principle
- Le Chatelier — a system at equilibrium shifts to relieve any applied stress (concentration, pressure or temperature).
8 — Effect of changing conditions
| Change | Shift |
|---|
| ↑ [reactant] | → right |
| ↑ pressure | → fewer gas moles |
| ↑ temperature | → endothermic direction |
| catalyst | no shift |
Only temperature changes the value of K.
9 — The Haber process (ammonia)
HaberN₂ + 3H₂ ⇌ 2NH₃ ΔH = −92 kJ (exothermic)
Use high pressure (4 moles → 2) and low temperature (exothermic). In practice ~200 atm, ~450 °C, iron catalyst — a compromise. Move the sliders to see the yield respond.
10 — The Contact process
Key step2SO₂ + O₂ ⇌ 2SO₃ (exothermic) · V₂O₅ catalyst
11 — Worked numericals
Kc
H₂ + I₂ ⇌ 2HI: Kc = [HI]²/([H₂][I₂]) = (2.0)²/(0.5×0.5) = 16
Le Chatelier
Raising T in N₂+3H₂⇌2NH₃ (exo) → less NH₃, Kc decreases.
12 — Exam recap
- Reversible vs irreversible; ⇌.
- Dynamic equilibrium & characteristics.
- Kc expression; Kp = Kc(RT)^Δn; size of K.
- Le Chatelier's principle.
- Effect of concentration, pressure, temperature, catalyst.
- Haber & Contact processes.