3.1.6 Equilibria

• All reversible reactions reach a dynamic equilbrium state
• Two features of dynamic equilibrium:

  1. Forward and backward reactions occuring at equal rates
  2. Concentrations of both reactants and products remain constant
• State Le Chatelier’s principle:

  "If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance"
• What is the effect of increasing temperature on equilibrium?

  • equilibrium shifts in the endothermic direction
  • tries to reduce temperature by absorbing heat
• What is the effect of decreasing temperature on equilibrium?

  • equilibrium shifts in the exothermic direction
  • attempts to increase temperature by giving out heat
• What is the effect of increasing pressure on equilibrium?

  • equilibrium shifts to the side with fewer moles
  • to oppose reduce change and reducing pressure
• What is the effect of decreasing pressure on equilibrium? 

  • equilibrium shifts to the side with more moles
  • to oppose the change and increase pressure
• If the number of mols of gas is the same on both sides of a reversible reaction, pressure will have no effect on the position of equilibrium. 
• Catalysts have no effect on position of equilibrium but speed up the rate at which equilibrium is achieved
• Catalysts work by providing an alternative reaction pathway wiith lower activation energy
• Activation energy: The minimum amount of energy needed for a reaction to occur with successful collisions
• The larger the Kc the greater the amount of products
• Temperature is the only external condition that affects value of Kc?
• Give an essential condition for an equilibrium mixture:

  
  

  Equilibrium occurs in a closed system (where reactants and products cannot escape)
• In this equation, what effect would increasing the temperature have on the position of equilibrium?

  
  

  The equilibrium position shifts to the right. (This is because the forward reaction is endothermic. Yield of hydrogen increases.)

  
• What effect would increasing the pressure have on the position of equilibrium?

  
  

  The equilibrium position shifts to the left.

  
  

  This is because the forward reaction is produces more moles of gas than the reverse reaction.

  
• What effect does a catalyst have on the position of equilibrium? No effect
• What type of system is Kc relevant for? Homogeneous systems in equilibrium
• What effect does decreasing the temperature in an exothermic reaction have on K c ?

  
  

  K c increases
• What effect does increasing the temperature in an exothermic reaction have on K c ?

  K c decreases