equilibrium

• when a reversible reaction occurs in apparatus which prevents the escape of reactants and products, equilibrium is reached when the FORWARD and REVERSE reactions occur at EXACTLY THE SAME RATE
• Le Chatelier's principle:

  If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change
• if the concentration of a reactant or product is changed, the system will counteract the change, so no longer at equilibrium, so the concentration of all substances will change until equilibrium is reached again
• increasing the concentration of a reactant = more product will be formed, until equilibrium is reached again
• if the concentration of a product is decreased = more reactants will react until equilibrium is reached again
• increasing the temp of system at equilibrium = counteracts change:

  • will shift to endothermic side, energy is taken in, to reduce the temp
• decreasing temp of system at equilibrium = counteracts change:

  • will shift to the exothermic side, energy is released, increase the temp
• increased temp:

  • the relative amount of products at equilibrium increases for an endothermic reaction
  • the relative amount of products at equilibrium decreases for an exothermic reaction
• decreased temp:

  • the relative amount of products at equilibrium decreases for an endothermic reaction
  • the relative amount of products at equilibrium increases for an exothermic reaction.
• pressure affects reactions involving gases

  it depends on number of molecules

  i.e. double moleculues = double pressure
• large numbers = number of molecules

  left side = 4 molecules

  right side = 2 molecules

  
• an increase in pressure on a reversible reaction in equilibrium, the equilibrium position will shift towards the side with the SMALLER NUMBER OF MOLECULES
• a decrease in pressure causes the equilibrium position to shift towards the side with a LARGER NUMBER OF MOLECULES
• in this case:

  increased pressure = shift to right

  decreased pressure = shift to left

  
• changing the pressure will have no effect on the position of equilibrium if the number of molecules are the same on both sides