chp 10

• reversible reaction


  products of the reactions can react to make the original reactants
• in a closed system the rate of the forward and reverse reactions are equal at equilibrium
• changing concentration

  if concentration of products builds up - the rate at which they react to reform reactants increase

  this means that the rate of the forward reaction decreases

  because the concentration of the reactants is decreasing from its original maximum value
• if the forward reaction produces more molecules of gas...

  ... an increase in pressure decreases the amount of products formed

  ... a decrease in pressure increases the amount of products formed
• if the forward reaction produces fewer molecules of gas ...

  ... an increase in pressure increases the amount of products formed

  ... a decrease in pressure decreases the amount of products formed
• if the forward reaction is exothermic ...

  ... an increase in temperature decreases the amount of products formed

  ... a decrease in temperature increases the amount of products formed
• if the forward reaction is endothermic ...

  ... an increase in temperature increases the amount of products formed

  .. a decrease in temperature decreases the amount of products formed
• Haber Process

  turning nitrogen into ammonia - used for fertilisers

  raw materials used are:

  • nitrogen from the air
  • hydrogen from methane

  the process:

  • a gas stream contains hydrogen and nitrogen
  • the nitrogen / hydrogen mixture is compressed to a pressure of 200 atm and heated to 450 ºC
  • reaction vessel contains the iron catalyst to speed up reaction
  • the mixture of gases emerging from the reactor is cooled, ammonia liquefies in the cooling chamber
  • unreacted nitrogen and hydrogen are returned to the reaction vessel via the compressor
• contact process

  makes sulfuric acid - used for paints, pigments, fertilisers, plastics, synthetic fibres, dydes

  raw materials:

  • sulfur
  • air
  • water

  stage 1:

  sulfur is burnt and oxidised to sulfur dioxide gas

  stage 2:

  sulfur dioxide is oxidised to make sulfur trioxide in a reversible reaction that takes place at 450 ºC and atmospheric pressure, in the presence of a vanadium oxide catalyst

  stage 3:

  in effect sulfur trioxide reacts with water to make sulfuric acid