Sign in

GCSE Science | Equilibrium

Last updated on 

Dynamic equilibrium

  • this is when the rate of forward reaction = rate of backward reaction
  • concentration of reactants and products stay the same
  • in a reversible reaction (⇌)
  • in a closed system
    • no substances are either added or escape from the system

Le Chatelier's Principle

  • if the conditions of a dynamic equilibrium are changed, the equilibrium will move to counteract the change
    • changes in temperature
    • changes in concentration of the reactants
    • changes in concentration of the products
    • changes in pressure

Examples - which way does equilibrium move?

  • an increase in temperature - endothermic direction
  • a decrease in temperature - exothermic direction
  • an increase in pressure - side with fewer molecules of gas
  • a decrease in pressure - side with more molecules of gas
  • an increase in concentration of reactants - right
  • a decrease in concentration of reactants - left
  • an increase in concentration of products - left
  • a decrease in concentration of products - right

Question 1

Question 2

Question 3

Question 4

Triple Science Only

Haber process

  • N2(g)+3H2​(g)⇌2NH3(g)
  • (The forward reaction is exothermic)
  • The process/ reaction used to produce ammonia
  • Rate of reaction - we want this to be fast
    • high pressure
    • high concentration
    • high temperature
  • Equilibrium - we want this to be shifted towards the right
    • high temperature - to shift equilibrium in exothermic direction
    • high pressure - to shift to side with fewer moles of gas
  • Overall compromise
    • high pressure - although expensive - 200 atm
    • temperature - 450o C - a compromise between faster rate and higher yield
    • iron catalyst

Contact process

  • 2SO2(g) + O2(g) ⇌ 2SO3(g)
  • (The forward reaction is exothermic)
  • Rate of reaction - we want this to be fast
    • high pressure
    • high concentration
    • high temperature
  • Equilibrium - we want this to be shifted towards the right
    • high temperature - to shift equilibrium in exothermic direction
    • high pressure - to shift to side with fewer moles of gas
  • Overall compromise
    • pressure - 2 atm - a higher pressure isn't needed as yield is already high. cheaper to use a low pressure.
    • temperature - 450o C - a compromise between faster rate and higher yield
    • vanadium oxide catalyst