Chapter 7: Equilibria
Dynamic Equilibrium
- Occurs in a closed system when forward and backward reactions happen at the same rate.
- Concentrations of reactants and products remain constant (but not necessarily equal).
- Example: Haber process (N₂ + 3H₂ ⇌ 2NH₃)
Characteristics
- Reversible reactions.
- No net change in macroscopic properties (colour, pressure, concentration).
- Reaction is still active at the microscopic level.
Le Chatelier’s Principle
- If conditions change, equilibrium shifts to oppose the change.
- Concentration: Adding reactants → shifts forward; removing reactants → shifts backward.
- Pressure: Increasing pressure favors side with fewer gas molecules.
- Temperature: Increasing temperature favors endothermic direction; decreasing favors exothermic.
- Catalysts: Speed up attainment of equilibrium but do not change position.
Equilibrium Constant (Kc)
- For reaction: aA + bB ⇌ cC + dD
Kc = {[C]^c [D]^d}/{[A]^a [B]^b}
- Depends only on temperature.
- Large Kc → products favored.
- Small Kc → reactants favored.
Industrial Applications
- Haber process: N₂ + 3H₂ ⇌ 2NH₃
- High pressure favors ammonia formation.
- Moderate temperature balances yield and rate.
- Iron catalyst speeds up reaction.
- Contact process: 2SO₂ + O₂ ⇌ 2SO₃
- Used in sulfuric acid manufacture.
- Vanadium(V) oxide catalyst employed.
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