Dynamic Equilibrium

Overview

• Focus on dynamic equilibrium in chemical systems.
• Importance of conditions for equilibrium.
• Examples of systems in equilibrium.

Key Concepts

Analogy of Digging a Hole

• Scenario:
  • You dig a hole, and your friend fills it.
  • If you dig faster, the hole increases in size.
  • If your friend fills faster, the hole decreases.
  • If both dig and fill at the same rate, the size remains constant.

Reversible Reactions

• Definition of Equilibrium:
  • When the rate of the forward reaction (reactants to products) equals the rate of the reverse reaction (products to reactants).
  • Dynamic Equilibrium:
    • Both processes happening simultaneously, with no observable change.

Criteria for Equilibrium

1. Reversible Process:
   • Must be able to go both ways (forward and reverse).
2. Closed System:
   • No exchange of matter; only energy exchange.

Example: Hydrogen and Iodine Reaction

• Reaction:
  • Hydrogen and iodine in a closed container produce hydrogen iodide.
  • Initially high concentration of hydrogen and iodine.
  • As hydrogen iodide forms, the concentration changes until they remain constant.
• Dynamic Equilibrium:
  • Forward reaction (forming hydrogen iodide) and reverse reaction (decomposition of hydrogen iodide) occur at the same rate.
  • No observable changes in concentrations, yet reactions continue.

Impact of Opening the System

• Scenario:
  • If the lid of the jar is removed, equilibrium is disrupted.
  • Reactants and products can escape, leading to a change in concentrations.

Phase Changes and Equilibrium

• Example:
  • Liquid bromine equilibrates to form gaseous bromine at room temperature.
  • Liquid bromine evaporates while gaseous bromine condenses.
  • Both processes occur at the same rate, resulting in no observable change but still achieving dynamic equilibrium.

Summary

• A chemical system reaches equilibrium when:
  • The rates of forward and reverse reactions are equal.
  • There are no observable macroscopic changes, indicating dynamic equilibrium.