Reversible Reactions and Equilibrium

Key Concepts

Reversible Reactions

• Single Arrow Reaction: Indicates a one-way reaction where reactants turn into products (e.g., carbon dioxide formation).
• Double Arrow Reaction: Indicates a reversible reaction where both forward and backward reactions can occur.
  • Forward Reaction: Ammonium chloride can break down into ammonia and hydrogen chloride.
  • Backward Reaction: Ammonia and hydrogen chloride can combine to reform ammonium chloride.

Equilibrium

• Definition: A state in a reversible reaction where the rate of the forward reaction equals the rate of the backward reaction.
• Characteristics:
  • Concentrations of reactants and products remain constant.
  • Reactions still occur but at equal rates, so there is no net change in concentrations.
  • Does not imply equal concentrations of reactants and products.

Position of Equilibrium

• Describes the relative amounts of reactants and products at equilibrium.
• Shifts in Equilibrium:
  • Right: More products than reactants.
  • Left: More reactants than products.
• Influence of Conditions:
  • Heat: Adding heat can shift equilibrium to the right (forward reaction).
  • Cooling: Lowering temperature shifts equilibrium to the left (backward reaction).
• Closed System Requirement: Equilibrium can only be achieved in a closed system where reactants and products cannot escape.

Thermodynamics of Reversible Reactions

• Exothermic and Endothermic:
  • All reversible reactions are exothermic in one direction and endothermic in the other.
  • Example: Thermal decomposition of hydrated copper sulfate:
    • Forward Reaction: Endothermic, requiring heat to decompose into anhydrous copper sulfate and water.
    • Backward Reaction: Exothermic, releasing energy when forming hydrated copper sulfate from anhydrous copper sulfate and water.

Recap

• Reversible reactions have both forward and backward reactions, one exothermic and the other endothermic.
• Equilibrium is achieved when forward and backward reaction rates equalize, maintaining constant concentrations of reactants and products.
• The position of equilibrium can shift based on environmental conditions.

End of Lecture