Equilibrium

• Define dynamic equilibrium.

  The rate of the forward reaction is equal to the rate of the reverse reaction and the concentration of the reactants and products remain constant in a closed system.
• Is there an observable change during dynamic equilibrium ?

  No
• If the PoE lies to the left, is the yeild of products high or low ?

  Low
• If the PoE lies to the right, is the yeild of products high or low ?

  High
• At equilibrium are the concentrations of reactants and products the same ?Why ?

  No, they just don't change
• What does Kc stand for ?

  equilibrium constant
• What is the equation for Kc ?

  Kc= Products / Reactants
• What type of brackets are used for a Kc equation ?What do they represent ?

  [] = Concentration
• What do you NOT include in a Kc expression ?

  Solids and liquids
• If Kc=1 , where does the PoE lie ?


  middle
• If Kc>1 , where does the PoE lie ?

  Right
• If Kc<1 , where does the PoE lie ?

  Left
• What 3 factors affect the PoE ?

  Concentration, Pressure and Temperature
• Why do catalysts not affect the PoE ?

  They speed up the rate of the forward and reverse reaction equally.
• Definition of Le Chatelier's Principle .

  When a system in dynamic equilibrium is subjected to change, the position of equilibrium shifts to reverse the change.
• Increasing the concentrations of the reactants favours the formation of what ?

  Products
• Increasing the concentration of products favours the formation of what ?

  Reactants
• Pressure only affects the equilibrium position of reactions involving what ?

  Gases
• What is pressure proportional to in an equilibrium ?

  number of moles
• If you increase the pressure what happens to the PoE ?

  PoE shifts to the side with fewer moles
• If you decrease the pressure what happens to the PoE ?

  PoE shifts to the side with more moles
• How will the PoE be affected if the number of moles of reactants is equal to the number of moles of products?

  No effect
• If the temperature is decreasing , what happens to the PoE ?

  PoE shifts to the exothermic side
• If the temperature is increasing, what happens to the PoE ?

  PoE shifts to the endothermic side
• Give an example of an industrial process which uses equilibrium processes.

  Haber Process
• Give the equation for the Haber process.

  N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
• Is the Haber Process exothermic or endothermic ?

  Exothermic
• Using Le Chatelier's Principle, predict the temperature that would produce a high yield of ammonia in the Haber process.

  If the temperature is decreased the PoE will shift to the right and favour the exothermic, forwards reaction. Therefore a low temperature will produce a high yield.
• What are the disadvantages of using low temperatures in industrial processes ?

  Slow rate of reaction and can't overcome the activation energy.
• Using Le Chatelier's Principle and collision theory, predict the pressure that will produce a high yield of ammonia in the Haber Process.

  There are 4 moles of gas on the LHS, but only 2 moles of gas on the RHS. If the pressure is increased the PoE will shift to the right where there are fewer moles, increasing the yield. Increasing the pressure means the molecules of gas are closer together and collide more frequently, therefore increasing the rate of reaction.
• What are the disadvantages of using high pressure ?

  It is dangerous and expensive to maintain.
• What is the purpose of the catalyst and how does it work?

  Purpose: Speed up forwards and reverse reaction equally and dynamic equilibrium is reached faster How: By lowering activation energy (providing an alternative pathway for the reaction)
• What was used in the Haber Process as a compromise for low temperature and high pressure? Why ?

  Catalyst - Allows lower temperatures to be used. Also less energy is needed to generate heat, so lower costs
• What are the units for Kc if there are 2 moles of products and 1 mole of reactants ?


  dm3mol-1