earths resources

• why is 450 degrees used in the harber process

  450°C is a compromise between percentage yield, rate of reaction, and cost.

  
  

  The forward reaction is exothermic, and so the reaction should be done at a low temperature to get a high yield.

  
  

  The reaction will be faster at higher temperatures because the particles will have more energy, and so will be more likely to collide with enough energy to react.

  
  

  Generating high temperatures is expensive, so we can't use a very high temperature.

  
  

  Iron catalyst increases yield but not rate of reaction
• what is potable water? Water which is safe to drink
• pure water = water without other molecules in it

  obtaining from fresh water: pass water through the fliter to remove large objects. Sterilise water using ozone, chlorine or uv.+
• to obtain potable water from sea water distillation or reverse osmosis is required. [expensive]

  Distillation - heating up sea water to seperate water and salt +

  Reverse osmosis - water is pressurised and passed through membranes which only water can go through, leaving salt and ions behind.
• metal extraction: phytomining and bioleaching

  Phytomining = plants are grown near the metal ore, when these are harvested and burnt the metal compound can be found in the ashes , this is extracted by electrolysis or displacement
• bioleaching = bacteria are added to the soil around the mine, they produce leachate containing the metal compound, this can be extracted by electrolysis or displacement
• life cycle assessment = assessing a products sustainability and impact on the environment.

  1. extraction of raw materials
  2. Maufacturing and packaging
  3. use and operation
  4. disposal at end of life
• Disposal of products

  1. add to landfill
  2. biodegrade = broken down by decomposers
  3. incinerated = burnt to release energy
  4. reused
  5. recycled
• Harber process = creating ammonia (used in fertilisers) from nitrogen and hydrogen in a reversible reaction.+

  1. nitrogen from the air and hydrogen from natural gas are pumped into the reactor which has a pressure of 200atm, 450degrees. +
  2. this goes through the reaction vessel which contains an iron catalyst (to increase yield)+
  3. unreacted nitrogen and hydrogen are transported back to the reaction vessel by the compressor+
  4. the gas leaving the reactor are cooled liquifying the ammonia so it can be seperated
• corrosion = the process by which a metal is gradually destroyed by chemical reactions with its surroundings, can be reduced by:

  1. physical barriers - layer of grease or paint or metal(electroplating)
  2. sacrifical methods - galvanising a metal with a more reactive metal so that will react with the environment instead
  3. Rusting - type of corrosion caused by iron reacting with oxygen and water from the environment.
• Alloys = mixture of metals to give ideal properties

  Gold - gold+copper/silver/zinc(hardness, less corrosion) - jewelery

  bronze - copper, tin (resistant to erosion) - used in statues/ decor

  brass - copper, zinc (hard) - taps, musical instruments

  aluminium - (low density - used in aircraft, military uses

  high carbon steel - iron + 1-2% carbon (strong) - cutting tools

  low carbon steel - iron + <1-2% carbon (soft, easy to shape) - cars, machienery

  stainless steel - iron+chromium+nickel ( hard + resistance to corrosion) - cutlery
• ceramics

  soda lime glass - heat mixture of sand sodium carbonate and limestone - transparent but brittle - glass

  borosilicate glass - heat sand+boron trioxide - high melting point - oven/lab glassware

  clay ceramincs - shape wet clay then heat in furnace - hard, easy to shape - pottery, bricks
• low density polyethene - addition polymerisation of ethene is carried out at high temperatures under small presence of oxygen. Branched polymer chains can't pack together causing low density+

  High density polyethene - addition polymerisation of ethene is carried out at 50degrees with a catalyst so polymer chains grow out straight and tightly packed together.
• thermosoftening polymers - don't have covalent bonds between chains so soften when heated

  thermosetting polymers - have strong covalent bonds between chains so do not melt when heated
• composite = making a material more useful by combining the main material(matrix) with fragments of other materials (reinforcements)