Overview
This lecture covers the fundamentals of chemical equilibrium, including dynamic equilibrium, Le Chatelier's Principle, how equilibria respond to condition changes, and industrial applications aimed at maximizing chemical yield.
Dynamic Equilibrium
- Many chemical reactions are reversible, proceeding both forwards and backwards.
- Dynamic equilibrium occurs in a closed system when the rate of the forward reaction equals the rate of the reverse reaction.
- At equilibrium, the concentrations of reactants and products remain constant, though not necessarily equal.
- The position of equilibrium varies and is not always 50/50 between reactants and products.
Le Chatelier's Principle
- Le Chatelier's Principle: "Equilibria shift to oppose change" when conditions (concentration, pressure, temperature) are altered.
- Increasing temperature shifts equilibrium toward the endothermic direction; decreasing temperature shifts it toward the exothermic direction.
- Increasing pressure shifts equilibrium toward the side with fewer moles of gas; decreasing pressure favors the side with more moles of gas.
- Increasing the concentration of a substance shifts equilibrium to reduce its concentration; decreasing it shifts equilibrium to increase its concentration.
- Catalysts speed up the rate of reaching equilibrium but do not affect the equilibrium position.
Types of Equilibria
- Homogeneous equilibrium: all reactants and products are in the same physical state (usually gas).
- Heterogeneous equilibrium: reactants and products are in different states (less relevant for this topic).
Industrial Applications
- Industrial processes often compromise between yield and reaction rate for practical efficiency.
- Methanol Synthesis: CO + 2H₂ ⇌ CH₃OH; high pressure (50-100 atm), moderate temperature (250°C), and a copper-based catalyst are used.
- Ethanol Synthesis: C₂H₄ + H₂O ⇌ C₂H₅OH; high pressure (60-70 atm), temperature around 300°C, phosphoric acid catalyst; recycle unreacted ethene for higher yield.
- Ammonia (Haber Process): N₂ + 3H₂ ⇌ 2NH₃; increased pressure and moderate temperature (~670 K, 20,000 Pa); higher yield at lower temperatures but slower rates.
Key Terms & Definitions
- Dynamic Equilibrium — A state where forward and reverse reactions occur at the same rate, keeping concentrations constant.
- Le Chatelier's Principle — Systems at equilibrium shift to oppose changes in conditions.
- Homogeneous Equilibrium — All reactants and products in the same physical state.
- Heterogeneous Equilibrium — Reactants and products in different states.
- Yield — The amount of desired product produced in a reaction.
Action Items / Next Steps
- Watch the next video on equilibrium constant ( K_c ) and related calculations.
- Review industrial process conditions and rationale for their specific choices.
- Practice questions on predicting equilibrium shifts under changing conditions.