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G11 s lequilibria

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G11 s lequilibria

  1. 1. + Equilibria Write the balanced equation for the synthesis of Ammonia Include Kc expression Include energy level diagram http://www.youtube.com/watch?v=uAJDD1_Oexo
  2. 2. + Aims  Introduce dynamic equilibria for both chemical and physical change.  Game 
  3. 3. + Definition 1 Chemical Equilibria http://www.youtube.com/watch?v=tlGrBcgA NSY&feature=related
  4. 4. +
  5. 5. + Definition 2  Physical Dynamic Equilibria.  i.e. water
  6. 6. + Definition 3  The ‘closed system’….  A closed system is one in which no substances are either aeddd to the system or lost from it. Energy can, however, beeerrransftdin or out at will.
  7. 7. + Summary  A dynamic equilibrium occurs when you have a verreslebi reaction in a closed system. Nothing can be dddae to the system or taken away from it apart fromregnye.  At equilibrium, the quantities of everything nresept in the mixture remain constant, although the reactions are stilluinitconng. This is because the rates of the forward and the back reactions arealeuq.
  8. 8. + Chemical Equilibria  http://www.youtube.com/watch?v=0XQVXFL4uoo  http://www.youtube.com/watch?v=GS9kIj9n- BU&feature=related
  9. 9. + The Equilibrium Constant  This is derived from concentrations – can be gases or liquids.  NB Always [products] / [reactants]  NB2 – this is for homogeneous reactions
  10. 10. + Magnitude of Kc  Kc is constant at constant T.  Changing Pressure or concentration or adding a catalyst do not change Kc.  If Kc>>1 – rxn goes to completion.  If Kc<<1 – rxn hardly proceeds.  If Kc 10-2 – 102 then [reactants] and [products] are present in the equilibirum mixture.
  11. 11. + Your Task  Who was Le Chatelier ?  What did he find out about equilibria ?  Discuss effect on Haber ( F ) or Contact ( M ) processes of altering the following ..  Temperature  Pressure  Concentration  Catalyst  MUST be communicated in an entertaining manner !  http://www.chem1.com/acad/webtext/chemeq/Eq-02.html#SEC1
  12. 12. + Key Concepts in Equilibria Equilibrium reactions are reversible chemical reactions. rate of the forward reaction = the rate of the reverse reaction At equilibrium the concentration of reactants / products does not change with time.  Catalysts do not affect the position of equilibrium  Heat increases the rate of both the forward and reverse reaction. Only closed systems can reach equilibrium.
  13. 13. + Le Chatelier’s Principle  When a system at equilibrium is disturbed, the equilibrium position will shift in the direction which tends to minimise, or counteract, the effect of the disturbance.
  14. 14. + Disturbances on Equilibrium * If the concentration of a solute reactant is increased, the equilibrium position shifts to use up the added reactants by producing more products. * If the pressure on an equilibrium system is increased, then the equilibrium position shifts to reduce the pressure. * If the temperature of an endothermic equilibrium system is increased, the equilibrium position shifts to use up the heat by producing more products. * If the temperature of an exothermic equilibrium system is increased, the equilibrium position shifts to use up the heat by producing more reactants.
  15. 15. + Effect of Catalyst  A catalyst speeds up the rate of both the forward and reverse reactions.  The initial slope of the concentration vs time lines will be steeper for both reactants and products.  A catalyst does NOT affect the equilibrium position.  At equilibrium the concentrations of reactants and products for the catalysed reaction are the same as for the uncatalysed reaction.