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 is a pungent smelling alkaline gas with the chemical formula NH3
  • Nitrogen gas (from the air) and hydrogen gas (from natural gas) react together to produce ammonia
  • The ammonia is collected by cooling the reaction mixture so the ammonia condenses into a liquid
  • The unreacted nitrogen and hydrogen are recycled back through the process, so there is no waste
• The Haber Process


  Nitrogen gas + Hydrogen gas → Ammonia
• Tests for ammonia gas and ammonium ions

  • Ammonia gas will change damp red litmus paper blue
  • Ammonium ions convert into ammonia gas which turns the damp red litmus paper blue
• The Chosen Reaction Conditions for the Haber Process


  • A compromise between the yield of production, rate of production, cost and safety
  • Lower temperature and higher pressure would produce the best theoretical yield
  • Higher temperature is a compromise between yield and rate
  • Higher pressures are expensive and have more risk of explosions, lower pressure is a compromise between yield and cost/safety
  • The catalyst speeds up the rate of production, without getting used up, but over time it gets poisoned and needs replacing
• The majority of ammonia and sulfuric acid produced is used to make fertilisers
• Ammonium sulfate


  Common fertiliser made by 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 process is in 3 stages with raw materials of sulfur, air and water
  • Stage 1: Sulfur burns in air to form sulfur dioxide gas
  • Stage 2: Sulfur dioxide reacts with more oxygen to form sulfur trioxide gas, this reaction is reversible and uses 400-500°C, atmospheric pressure and a vanadium(V) oxide catalyst
  • Stage 3: Sulfur trioxide is dissolved in concentrated sulfuric acid to produce oleum, which is then diluted with water to produce sulfuric acid
• Adding sulfur trioxide directly to water is too violent
• Concentrated sulfuric acid as a dehydrating agent

  It removes water from a substance, like in the reaction with glucose where it takes away the elements of water leaving only carbon, with the water removed as steam because the reaction is exothermic