Lesson 1: Intro to Equilibrium

• Irreversible chemical reactions

  Highly exothermic reactions where the activation energy for the reverse reaction is extremely high
• Irreversible reaction

  • C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)
• Irreversible reactions

  • Only go in a forward direction, you can't get the reactants back after the products are formed
• Reversible reactions

  Products can form reactants, giving rise to an equilibrium where both reactants and products are present
• Reversible reactions are important in industrial processes
• Dynamic equilibrium

  An equilibrium where both forward and reverse reactions are occurring at equal rates in a closed system with no net change in concentration
• Establishing equilibrium

  1. Forward reaction is faster than reverse at start

  2. Forward reaction slows down as reactants used up, reverse speeds up

  3. At equilibrium, forward and reverse rates are equal
• Law of equilibrium

  At equilibrium, there is a constant ratio between the concentration of the products and reactants
• Equilibrium constant (Keq or K)


  A mathematical expression representing the ratio of product concentration to reactant concentration, with each concentration raised to the power of the coefficient
• Pure liquids and solids are not included in the equilibrium constant expression, only gases and solutions are included
• The value of K can indicate whether the formation of reactants or products is favoured

  K > 1 means products are favored

  K < 1 means reactants are favored

  K = 1 means neither are favored
• Percent reaction is also an indicator of whether reactants or products are favoured

  • > 50% , products are favored
  • < 50% , reactants are favored
  • = 50 % , neither reactants nor products are favored