Module 3.2.3- Chemical equilibrium

• 3 features of dynamic equilibrium

  closed system

  rate of forward reaction = rate of reverse reaction

  concentrations of products and reactants do not change
• le Chatelier's principle


  when a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change
• le Chatelier's principle: concentration

  Increase reactants: favour products to decrease reactant conc. (equilibrium shifts to the right)Increase products: favour reactants to decrease product conc. (equilibrium shifts to the left)
• le Chatelier's Principle: Temperature

  Increasing temperature shifts equilibrium in the endothermic direction to absorb the heat (and vice versa)
• le Chatelier's Principle: pressure

  Increase the pressure: favour side with fewest amount of moles to decrease it

  Decrease the pressure: favour side with more moles to increase it
• Effect of catalyst on equilibrium

  no change in the position of equilibrium

  speeds up the rate of forward and reverse reactions equally

  increases the rate an equilibrium is established
• 3.2.3d)

  "the techniques and procedures used to investgate changes to the positon of equilibrium for changes in concentraton and temperature"
• Kc equation

  [products]/[reactants]must be square brackets!

  
• Kc value of 1 indicates

  position of equilibrium is halfway between reactants and products
• Kc value of > 1 indicates

  position of equilibrium that is towards the products
• Kc value of < 1 indicates

  position of equilibrium that is towards the reactants