The complete lecture β 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 β Reversible & irreversible reactions
- Reversible reaction β proceeds in both directions; shown with β, e.g. Nβ + 3Hβ β 2NHβ.
2 β Dynamic equilibrium
- Equilibrium β forward rate = reverse rate; concentrations stay constant. It is dynamic β both reactions continue.
3 β Characteristics of equilibrium
- Closed system; dynamic; constant concentrations.
- Reached from either side; a catalyst changes only the speed.
4 β Law of mass action & Kc
aA + bB β cC + dDKc = [C]αΆ[D]α΅ / [A]α΅[B]α΅
5 β Kp and its relation to Kc
LinkKp = Kc (RT)^Ξn (Ξn = gas moles products β reactants)
6 β The significance of K
| K | Means |
|---|
| β« 1 | products favoured |
| β 1 | both present |
| βͺ 1 | reactants favoured |
7 β Le Chatelier's principle
- Le Chatelier β a system at equilibrium shifts to relieve any applied stress (concentration, pressure or temperature).
8 β Effect of changing conditions
| Change | Shift |
|---|
| β [reactant] | β right |
| β pressure | β fewer gas moles |
| β temperature | β endothermic direction |
| catalyst | no shift |
Only temperature changes the value of K.
9 β The Haber process (ammonia)
HaberNβ + 3Hβ β 2NHβ ΞH = β92 kJ (exothermic)
Use high pressure (4 moles β 2) and low temperature (exothermic). In practice ~200 atm, ~450 Β°C, iron catalyst β a compromise. Move the sliders to see the yield respond.
10 β The Contact process
Key step2SOβ + Oβ β 2SOβ (exothermic) Β· VβOβ
catalyst
11 β Worked numericals
Kc
Hβ + Iβ β 2HI: Kc = [HI]Β²/([Hβ][Iβ]) = (2.0)Β²/(0.5Γ0.5) = 16
Le Chatelier
Raising T in Nβ+3Hββ2NHβ (exo) β less NHβ, Kc decreases.
12 β Exam recap
- Reversible vs irreversible; β.
- Dynamic equilibrium & characteristics.
- Kc expression; Kp = Kc(RT)^Ξn; size of K.
- Le Chatelier's principle.
- Effect of concentration, pressure, temperature, catalyst.
- Haber & Contact processes.