Topic 4: Gases, Equilibria and Ammonia

Topic 4: Gases, Equilibria and Ammonia

1. The Harber process

   • Fritz Harber, 1900's
   • Uses the reversible reaction of ammonia- the conditions allow the forward reaction to happen faster than the backward reaction as it is in equilibirum
   • 200 atmospheres, 450 ' C, iron catalyst

2. Molar volume of gases

   • Avogadro's gas law- 1 mole of any gas at room temperature and normal atmospheric pressure has a volume of 24dm'3
   • using the idea of molar volume we can calculate volumes of gases needed for reactions
     • e.g. how much methane (CH4) is burned completely in oxygen if 11g of CO2 is produced?
       • 1. balanced symbol equation, 2. work out number of moles in 11g of CO2, 3. work out molar ratio of methane to CO2,4 . number of moles x molar volume
   • volume (dm'3) = number of moles x molar volume of gas (dm'3)

3. Reversible reactions

   • A + B <> C + D
   • The products of a reaction will react to give the original reactants back
   • ammonium chloride + HEAT <<>> Ammonia + Hydrogen Chloride

4. Equilibrium

   • The forward and backward reactions happen at the same rate.
   • decreasing the temperature for the ammonia reaction will result in an increase of the rate of forward reaction because it is exothermic - heats up
     • 'equilibirum has shifted to the right'
   • increasing pressure results in a higher yield of ammonia as the equilibrium again shifts to the right. This is to expensive, it is done at 200 at

5. Fertilisers

   • Over-use of nitrate fertilisers leads to Eutrophication
   • contain soluble nitrogen compounds which plants need to make proteins
   • Ammonia is a raw material used to make nitrogenous fertilisers
   • advantages of manmade- easy to store, distribute and handle, produced to match requirements, increase yield of crops
   • disadvantages of over use- high nitrate levels are dangerous in drinking water, eutrophication