Reversible Reactions and Equilibrium

Reversible Reactions

  • Reversible reactions are indicated by the symbol ⇌ in equations.
  • Examples:
    • Dehydration of hydrated copper(II) sulphate
    • Effect of heat on ammonium chloride
  • Dynamic equilibrium concept
  • Le Chatelier's Principle: Predict the effects of changing pressure and temperature on equilibrium position.

Symbol for Reversible Reaction

  • The symbol indicates that a reaction can proceed in both directions.

Definition of Reversible Reaction

  • A reversible reaction can go in both directions.
  • Products can be turned back into original reactants.

General Equation

  • A + B \rightleftharpoons C + D
  • A and B react to produce C and D, and C and D can react to produce A and B.

Example 1: Heating Blue Copper Sulphate

  • Heating blue hydrated copper sulphate produces water vapor and white anhydrous copper sulphate.
  • CuSO4.5H2O(blue) \rightleftharpoons CuSO4(white) + 5H2O
  • Adding water to white anhydrous copper sulphate turns it back into blue hydrated copper sulphate.

Example 2: Thermal Decomposition of Ammonium Chloride

  • The Thermal Decomposition of ammonium chloride: NH4Cl
  • NH4Cl \rightleftharpoons NH3 + HCl
    • When heated, solid ammonium chloride splits into ammonia gas and hydrogen chloride gas.
    • As the gases cool, they recombine to form solid ammonium chloride.
    • This is a good example of a reversible reaction because the products recombine easily to form the original reactants.

Reversible Reactions and Closed Systems

  • Dynamic Equilibrium: A chemical equilibrium between a forward reaction and the reverse reaction where the rates of the reactions are equal.
  • At dynamic equilibrium, the ratio between reactants and products remains unchanged over time.
  • Imagine a closed system where no more reactants are added, and no products are removed.
  • A + B \rightleftharpoons C + D
  • A and B combine to form C and D, while C and D combine to form A and B.
  • A point will eventually be reached when the rate of the forward reaction is equal to the rate of the backward reaction. This point is known as the dynamic equilibrium.

Le Chatelier's Principle

  • Le Chatelier's principle states that