EQUILIBRIUM IN MORE DETAIL

• Reversible reactions


  Reactions where the products can react to produce the original reactants
• Reversible reactions


  Reaction can be changed by changing conditions (e.g. hot for forwards, cool for reverse)
• Reversible reaction symbol


  ⇌ (instead of →)
• Example of reversible reaction


  • Hydrogen + Nitrogen ⇌ Ammonia (Haber Process)
• If a reversible reaction is endothermic one way


  It is exothermic in the opposite direction
• The same amount of energy is transferred each way in a reversible reaction (just lost one way, gained the other)
• Equilibrium


  When a reversible reaction occurs in a closed system, equilibrium is reached when the reactions occur at exactly the same rate in each direction
• If a change is made to the conditions of a system at equilibrium

  The system responds to counteract the change (Le Chatelier's principle)
• If the concentration of one of the reactants or products is changed

  The system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again
• If the concentration of reactants is increased


  The position of equilibrium shifts towards the products so more product is produced until equilibrium is reached again
• If the concentration of products is increased


  The position of equilibrium shifts towards the reactants so more reactant is produced until equilibrium is reached again
• If temperature is increased


  Equilibrium moves in the direction of the endothermic reaction
• If temperature is decreased


  Equilibrium moves in the direction of the exothermic reaction
• Effect of temperature on yield for exothermic and endothermic reactions

  • Exothermic: Increase in temperature decreases yield, Decrease in temperature increases yield
  • Endothermic: Increase in temperature increases yield, Decrease in temperature decreases yield
• In gaseous reactions, if pressure is increased


  The equilibrium shifts to the side of the equation with the least number of moles of gas
• In gaseous reactions, if pressure is decreased


  The equilibrium shifts to the side of the equation with the most number of moles of gas
• Effect of pressure on yield for reactions with more or fewer moles of gas

  • Reaction produces larger volume of gas (more moles): Increase in pressure decreases yield, Decrease in pressure increases yield
  • Reaction produces smaller volume of gas (fewer moles): Increase in pressure increases yield, Decrease in pressure decreases yield