Reversible Reactions

Understanding Reversible Reactions

  • A reversible reaction is one where the reactants can reform from the products if conditions are changed.
  • Reversible reactions are signified in chemical equations by the reaction arrow direction changing from right to left and left to right like this: ⇌
  • In a closed system, the forward and reverse reactions continue to happen, resulting in an equilibrium being established.

Dynamic Equilibrium

  • A dynamic equilibrium is reached when the rate of the forward reaction equals the rate of the back reaction.
  • At dynamic equilibrium, the concentrations of the reactants and products remain constant although the transformation between reactants and products continues.
  • The quantitative study of these situations is referred to as chemical equilibrium.

Factors Affecting Equilibrium: Le Chatelier’s Principle

  • Le Chatelier’s Principle states that if a change in conditions is imposed on a system at equilibrium, the position of equilibrium will shift to counteract the change.
  • Pressure: If you increase the pressure, the reaction will favour the side with less volume (fewer gaseous molecules) to decrease the pressure. If you decrease the pressure, it will favour the side with more volume (more gaseous molecules) to increase the pressure.
  • Temperature: If you increase the temperature, the reaction will favour the endothermic side to absorb the heat and cool down. If you decrease the temperature, it will favour the exothermic side to release heat and warm up.
  • Concentration: If you increase the concentration of the reactants, more products will be formed to reduce this concentration. If you increase the concentration of the products, more reactants will be formed to reduce this concentration.

Industries and Reversible Reactions

  • Reversible reactions play a significant role in industrial processes because they allow for recycling of reactants and hence improved process efficiency.
  • The Haber process (ammonia synthesis) and Contact process (sulfuric acid production) are examples of industrial processes that use reversible reactions.
  • Industrially, conditions are chosen to maximise yield, while considering factors such as cost, rate of reaction, and environmental considerations.