Haber process and fertilisers

• nitrogen and hydrogen are needed to make...

  ammonia
• Haber process


  an industrial process for producing ammonia from nitrogen and hydrogen by combining them under high pressure in the present of an iron catalyst
• ammonia equation


  nitrogen + hydrogen ⇌ ammonia

  N2 + 3H2 = 2NH3
• where is nitrogen obtained for the Haber process?

  it is obtained easily from the air, which is 78% nitrogen. fractional distillation of liquid air is performed to extract it from the air
• where is hydrogen obtained for the Haber process?

  it mainly comes from reacting methane (from natural gas) with steam to form hydrogen and carbon dioxide. steam-methane reforming is performed to extract it from natural gas
• what are ammonia's reactant gases passed over?

  an iron catalyst
• what temperature is used to make ammonia?

  450°C
• what pressure is used to make ammonia?

  200 atmospheres
• because the reaction to make ammonia is reversible...

  some of the ammonia produced converts back into hydrogen and nitrogen again. it eventually reaches a dynamic equilibrium
• ammonia is formed as a...

  gas
• how does ammonia become liquid?

  it cools in a condenser
• what happens to unused hydrogen and nitrogen?


  they are recycled so nothing is wasted
• what is ammonia used for?

  fertilisers, refrigerant gas, for purification of water supplies, and in the manufacture of plastics, explosives, textiles, pesticides, dyes and other chemicals
• what is most of the produced ammonia used for?

  fertilisers
• the forward reaction in the Haber process is...

  exothermic

  - this means that at lower temperatures the yield is greater because the equilibrium shifts to the product's side
• the yield of ammonia is greater at ... temperatures


  lower
• why is 450°C used in the Haber process?

  high enough to sustain a reasonable rate, but not too high to reduce the equilibrium yield. also low enough to maximise yield but not too low to decrease the rate of reaction
• the yield of ammonia is greater at ... pressure

  higher
• why is 200 atmospheres used in the Haber process?


  the pressure is set as high as possible without making the process too expensive or dangerous to build and run
• increasing temperature and pressure both...

  increase rate of reaction
• does the presence of a catalyst affect the yield?


  no
• fertilisers help us...


  produce more food by allowing us to keep growing crops on the same land every year
• what are fertilisers?

  natural or artificial materials that are added to soils to provide essential nutrients and improve plant growth
• why are formulated fertilisers better than manure?

  they're more widely available, easier to use, don't smell and have just enough of each nutrient so more crops can be grown
• the three main essential elements in fertilisers are...

  nitrogen, phosphorus and potassium
• why are nitrogen, phosphorus and potassium used in fertilisers?

  because these elements may be missing from the soil if they've been used up by a previous crop
• what happens if plants don't get enough of the fertilisers' essential elements?

  their growth and life processes will be affected
• how do fertilisers increase crop yield

  fertilisers provide nutrients for the plant

  which are needed for growth to make the

  crops large and give a plentiful yield
• why do plants need nitrogen?

  to make proteins for growth
• why do plants need phosphorus?

  to make DNA and cell membranes
• why do plants need potassium?

  to make enzymes for aerobic respiration and photosynthesis
• what are NPK fertilisers?

  formulations containing salts of nitrogen (N), phosphorus (P) & potassium (K), the three main essential elements in fertilisers, in the right percentage of the elements
• ammonia is used to produce...

  nitrogen containing compounds
• how is nitric acid formed?

  ammonia can be reacted with oxygen and water in a series of reactions to make nitric acid
• how are ammonium salts formed?

  when acid reacts with aqueous ammonia
• how is ammonium nitrate formed?

  by neutralising ammonia with nitric acid (neutralisation reaction)
• why is ammonium nitrate formed?

  because it has nitrogen from two sources
• how are fertilisers formed in industry?

  1) the reaction is carried out in giant vats, at high concentrations resulting in a very exothermic reaction

  2) the heat released is used to evaporate water from the mixture to make a very concentrated ammonium nitrate product
• how are fertilisers formed in the lab?

  1) the reaction is carried out on a much smaller scale by titration and crystallisation

  2) the reactants are at a much lower concentration than in industry, so less heat is produced by the reaction and it's safer for the a person to carry it out

  3) after the titration, the mixture then needs to be crystallised the give pure ammonium nitrate crystals

  4) crystallisation isn't used in industry because it's very slow
• phosphate and potassium are sourced from...

  mined compounds and can be used directly without any further processing