chem topic 8

• cracking

  a process of thermal decomposition where the breakdown of long alkane hydrocarbons into a shorter alkene + alkane molecule
• thermal decomposition

  is where 1 substance w/ v strong covalent bond is broken down into 2+ new + more useful substances by heating. it requires a lot of energy to break the bonds so a catalyst is often used.
• example of a long alkane in cracking

  bitumen + fuel from fractional distillation of CO
• example of a smaller alkene + alkane in cracking

  petrol + diesel - more demand for them

  the alkene is also used to make polymers
• vaporized alkane runs of a powdered catalyst - AlO2 - at high temp + pressure

  alkane cracks on the surface when it comes into contact w/ the catalyst
• how was the earth's early atmosphere formed

  by gases produced by volcanic activity
• earth's early atmosphere

  • earth was a hot ball of magma eventually earth cooled + a crust was formed. but volcanic activity released lots of CO2 (+ H2O, NH3, CH4, v little O2)
  • condensation of water vapour --> oceans
• green plants evolved

  1. ↑N2 - formed NH4 + O2 reacting + denitrifying bacteria releasing it. Not v reactive so wasn't broken down after being made
  2. ↓ CO2 bc dissolved into the oceans + removed by plants in photosynthesis + CO2 locked in fossil fuels + sedimentary rocks
  3. ↑ O2 - released by plants
• todays atmosphere

  • build up of O2 nearly caused extinction of lots of organisms but lots of organisms evolved to it + used O2.
  • O2 built up the ozone layer which prevented harmful rays entering the earth's atmosphere, allowing more organisms to evolve
  • no CO2 rlly left
• test for O2

  glowing splint relights
• how did the amount of CO2 decreased

  • dissolved into the oceans
  • removed by plants in photosynthesis
  • locked in fossil fuels + sedimentary rocks
• what is the greenhouse effect - good

  • when CO2, CH4, water vapour absorb heat released by the earth
  • they then release energy that keeps the earth warm enough for us to live on
• how has ↑ population affected levels of CO2

  • ↑ human population, ↑ need for energy, ↑ use of fossil fuels, ↑CO2 released.
  • deforestation - to provide land (food + homes) for ↑ human pop, ↓ trees which absorb CO2
• enhanced greenhouse radiation - (bad)


  where the earth absorbs too much heat radiation and less is re-emitted into space. this cause atmosphere to heat up (climate change)
• methane

  • a v effective greenhouse gas
  • released from the digestive processes of livestock
  • ↑human pop=↑livestock= ↑methane released
• global warming


  human activity causing average temperature ↑ bc of the enhanced greenhouse effect

  type of climate change that causes over types of climate change. e.g severe flooding bc melting ice caps
• historical data

  • tree rings
  • fossils
  • gas bubbles in ice sheets
• historical data what they r used for and - ives

  used to estimate past CO2 levels as there were no records of it in the past

  they r less pescise then current measurements+↓ representative of global levels then current records r
• to slow down climate change

  1. ↓ fossil fuel usage - ↓ CO2 emissions
  2. gov told us to be more energy efficient+ r researching into more renewable energy sources