10.4 - Factors Affecting Equilibria

• Le Chatelier's Principle

  if there's a change in concentration, pressure, or temperature, equilibrium moves to counteract the change
• what happens if equilibrium shifts to the left?

  you get more reactants
• what happens if equilibrium shifts to the right?

  you get more products
• effect of increasing concentration of reactants on the position of equilibrium

  equilibrium shifts to the right to use up the reactant so more product is made

  favours forward reaction
• effect of increasing concentration of products on the position of equilibrium

  equilibrium shifts to the left so product is used up and more reactants are made

  favours the backward reaction
• effect of decreasing the concentration of reactants on the position of equilibrium

  equilibrium shifts to the left to use more products so make more reactants

  favours backward reaction
• effect of decreasing concentration of products on the position of equilibrium

  equilibrium shifts to the right so more reactants are used up to make more products

  favours forward reaction
• effect of increasing pressure on the position of equilibrium

  shifts equilibrium to the side with fewer gas molecules so less molecules are produced so less molecules in the container thus lowering the pressure
• effect of decreasing pressure on the position of equilibrium

  shifts equilibrium to the side with more gas molecules so more molecules are produced so pressure increases
• effect of increasing temperature on the position of equilibrium

  equilibrium shifts to favour the endothermic reaction to absorb heat
• effect of decreasing temperature on the position of equilibrium

  equilibrium shifts to favour exothermic reaction to release heat
• conditions for the Harber process

  iron catalyst with potassium hydroxide as a promoter

  200 atmospheres

  400-450 degrees
• why is a pressure of 200 atmospheres used in the Harber process?

  4 moles on the right, 2 on the left

  so higher pressure shifts equilibrium to the right and increases rate of reaction so higher yield of ammonia
• why is a temperature of 400-450 degrees used in the Harber process?

  forward reaction is exothermic so lower temeperature favour production of ammonia

  but lower temperatures decrease rate of reaction

  so 400-450 is a compromise between high yield and fast rate of reaction
• why is an iron catalyst used in the Harber process?

  doesn't affect position of equilibrium

  increases rate of reaction so equilibrium is reached faster
• conditions for the manufacture of ethanol

  60-70 atmospheres

  300 degrees

  phosphoric (V) acid catalyst
• why is a temperature of 300 degrees used in the manufacture of ethanol?

  forward reaction is exothermic so lower temperatures favour it

  but it reduces rate of reaction

  so 300 is a compromise between high yield and fast reaction
• why is a pressure of 60-70 atmospheres used in the manufacture of ethanol?

  high pressure favours forward reaction as equilibrium shifts to the right due to fewer moles

  but it's expensive to maintain and may polymerise ethene si 60-70 atm is a compromise
• why is a phosphoric (V) acid catalyst used in the manufacture of ethanol?

  increases rate of attainement of equilibrium without affecting its position