Reversible reactions

• Reversible Reaction


  A reaction that happens in both directions. This means the products of the reaction can react together to produce the original reactants.
• ⇌


  The symbol used to represent a reversible reaction
• If the forward reaction is exothermic


  The reverse reaction is endothermic
• The Haber Process


  Used in the industrial production of ammonia
• Ammonia


  A pungent smelling alkaline gas with the chemical formula NH3
• The Haber Process


  1. Nitrogen gas (from the air) and hydrogen gas (from natural gas) react together to produce ammonia

  2. The ammonia is collected by cooling the reaction mixture so the ammonia condenses into a liquid

  3. The unreacted nitrogen and hydrogen are recycled back through the process, so there is no waste
• The reaction conditions for the Haber Process are a compromise between the yield of production, rate of production, cost and safety
• Lower temperature and higher pressure

  Produce the best theoretical yield of ammonia
• Higher temperature


  Is a compromise between yield and rate of production
• Higher pressures


  Are expensive and have more risk of explosions
• Lower pressure


  Is a compromise between yield and cost/safety
• Catalyst


  Speeds up the rate of production, without getting used up, but over time gets poisoned and needs replacing
• Fertilisers


  The majority of ammonia and sulfuric acid produced is used to make fertilisers
• Making ammonium sulfate fertiliser

  Neutralising sulfuric acid with ammonia or ammonium hydroxide
• Advantages of fertilisers


  • Increases crop yield
  • Healthier crops
  • Improves soil quality
• Disadvantages of fertilisers


  • Eutrophication
  • Risk of stomach cancer
  • Blue baby syndrome
• The Contact Process


  Used in the industrial production of sulfuric acid, H2SO4
• The Contact Process


  1. Stage 1: Sulfur burns in air to form sulfur dioxide gas

  2. Stage 2: Sulfur dioxide reacts with more oxygen to form sulfur trioxide gas

  3. Stage 3: Sulfur trioxide is dissolved in concentrated sulfuric acid to produce oleum, which is then diluted with water to produce sulfuric acid
• The reaction in Stage 2

  Is reversible
• Conditions in Stage 2

  400 – 500OC, Atmospheric pressure, Vanadium(V) oxide catalyst
• Concentrated sulfuric acid


  A dehydrating agent that removes water from substances
• Dehydration of glucose by concentrated sulfuric acid


  The concentrated sulfuric acid takes away the elements of water leaving only carbon, with the water removed as steam because the reaction is exothermic
• Ammonia gas


  Changes damp red litmus paper blue
• Testing for ammonia gas and ammonium ions

  1. add sodium hydroxide solution

  2. test the gas with damp red litmus