EQUILIBRIUM

Le Chatelier's Principle

• States that if a stress is applied to a system in equilibrium, the system will adjust to counteract that stress and restore equilibrium.

Types of Stress and Their Effects

1. Changing Concentration

• Adding Reactants: Increases concentration on the reactant side.

  • Equilibrium shifts right to use up additional reactants, producing more products.

• Adding Products: Increases concentration on the product side.

  • Equilibrium shifts left to use up additional products, producing more reactants.

• Removing Components: Selectively removing a component will cause equilibrium to shift toward producing more of that component to restore balance.

2. Changing Temperature

• Determined by the enthalpy change (Delta H).

  • Exothermic Reactions (Delta H < 0): Heat is a product.

    • Increasing temperature shifts equilibrium left to absorb excess heat.

  • Endothermic Reactions (Delta H > 0): Heat is a reactant.

    • Increasing temperature shifts equilibrium right to use up excess heat.

3. Changing Volume and Pressure

• Uses Boyle's Law: Decreasing volume increases pressure.

• Low Volume/High Pressure: If equilibrium has unequal moles of gas:

  • Shifts toward fewer moles side to relieve pressure (e.g., from two monoatomic species to diatomic).

• High Volume/Low Pressure: Shifts toward more moles side to regain pressure.

Summary

• Le Chatelier's Principle helps predict the direction of equilibrium shifts when a stress such as concentration, temperature, or pressure is applied to a system.