Free Science Lessons: Reversible Reactions and Equilibrium

Key Learning Objectives

• Describe what is meant by a reversible reaction.
• Understand the concept of equilibrium.
• Describe energy changes in reversible reactions.

Reactions Overview

• Irreversible Reaction Example:

  • Reaction: Magnesium + Oxygen → Magnesium Oxide
  • Characteristics: One-way arrow indicating the reaction only goes forward. Magnesium oxide cannot revert to magnesium and oxygen.

• Reversible Reaction Example:

  • Reaction: Ammonium Chloride ⇌ Ammonia + Hydrogen Chloride
  • Characteristics: Double arrow indicating the reaction can proceed in both directions.
  • Changing Conditions:
    • Heating drives the forward reaction.
    • Cooling drives the reverse reaction.

Energy Changes in Reversible Reactions

• Hydrated Copper Sulfate Example:

  • Reaction: Hydrated Copper Sulfate (blue) + Heat → Anhydrous Copper Sulfate (white) + Water
  • Forward Reaction:
    • Endothermic: Energy is absorbed when converting to anhydrous copper sulfate.
  • Reverse Reaction:
    • Exothermic: Energy is released when adding water back to anhydrous copper sulfate, making it hot.

• Key Point:

  • If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction.
  • The same amount of energy is transferred in both directions.

Equilibrium

• Definition: Equilibrium occurs when the forward and reverse reactions take place at the same rate in a sealed container.
  • No reactants or products escape from the container.
  • Important for understanding how reactions balance under certain conditions.

Exam Tips

• Learn the copper sulfate reaction as it is frequently asked in exams.
• Use the revision workbook for practice questions on reversible reactions.

These notes summarize the key concepts of reversible reactions, energy changes, and equilibrium as discussed in the lecture. They provide a foundation for further study and exam preparation on this topic.