Equilibria

• ICEE equations for Kc questions

  I is the initial moles

  C is the change of moles

  E is the equilibrium moles

  E is the equilibrium concentration
• Le Chatelier's principle

  "If a factor affecting the position of an equilibrium is altered the position of the equilibrium shifts to oppose the effect of the change"
• Le Chatelier's questions

  1. First state what happens to yield
  2. State why is it happening
  3. State which direction would equilibrium shifts
  4. State to oppose the change in the question
• Dynamic equilibrium

  It's where both forwards and reverse reactions occur at the same time.
• Changing Temperature(increasing)

  Increasing temperature causes equilibrium to shift to direction where the endothermic reaction is (+ve ∆H) because excess heat needs to be removed from the system to lessen the effect of the initial increase. It will increases the yield of the endothermic products
• Changing temperature (decreasing)

  Decreasing temperature favours the exothermic reaction (negative ∆H) as heat needs to be gained and will increases the yield of the exothermic products
• Decreasing pressure

  Equilibrium favours the side of the reaction with more moles to increase pressure as there would be more molecules in a given area. The yield of the products on this side of the reaction will be increased.
• Catalysts do not affect the equilibrium position as they affect the forward and reverse reactions equally, allowing the equilibrium to be approached faster.
• The value of Kc is not affected by concentration change or use of a catalyst but is affected by changing temperature
• Reversible reaction, le Chatelier's principle example

  A (aq) + B (aq) ⇌ C (aq) + D (aq)

  If more A or B is added then the forward reaction increases and the equilibrium will shift to the right, reducing the concentration of A and producing more C and D
• If Kc is above 1

  There will be more products than reactants and the equilibrium position will be to the right
• If Kc is below 1

  There will be more reactants than products and the equilibrium position will be to the left
• Equilibrium can only occur when the reaction takes place in a closed system/container
• Kc formula

  aA + bB ⇌ cC + dD

  Kc = [C]^c × [D]^d ÷ [A]^a × [B]^b

  So it's the concentration of the substance to the power of the balancing numbers measured in moldm^-3

  products / reactants
• Increasing concentrations of reactants

  A + B  ⇌ C + D

  Increasing conc of reactants would cause equilibrium to shift to the right to oppose the change so more products is produces and the reactants are used up
• Increasing pressure

  A + B  ⇌ 4C +2D

  Favours the side of the reaction with fewer moles so equilibrium would shift to the left as there would be fewer molecules in a given area so it decreases pressure . It will increase the yield of the products on this side of the reaction.