chemistry module one

evolution of the atmosphere
1. phase one
  1. the earth's surface was originally molten for millions of years.
    1. so hot that any atmosphere just boiled away into space
  2. eventually things cooled down a bit & a thin crust formed but volcanoes kept erupting
    1. volcanoes gave out lots of gas- like carbon dioxide, water vapour and nitrogen
  3. according to this theory the early atmosphere was probably mostly CO2 and water vapour with virtually no oxygen
2. phase two
  1. green plants evolved and produced oxygen over most of the earth, through photosynthesis
    1. a lot of the early CO2 dissolved into the oceans.
    2. when plants died and were buried under layers of sediment the carbon they'd removed from the air as CO2 became locked up in sedimentary rocks as insoluble carbonates & fossil fuels
3. phase three
  1. build up of oxygen in the atmosphere killed off some early organisms that couldn't tolerate it
    1. allowed more complex organisms to evolve
    2. virtually no CO2 now
atmosphere now
1. nitrogen 78%
  1. oxygen 21%
  2. Argon <1%
2. human activity is changing the atmosphere
  1. human activity is adding small amounts of pollutants into the air
    1. carbon dioxide, carbon monoxide, particulates, sulphur dioxide, nitrogen oxides
      1. sulphur dioxide can cause acid rain
        pollutes rivers and lakes, killing fish which people catch and eat
  2. other pollutants are leading to climate change
    1. rising sea levels, change in climate etc
fossil fuels
1. majority of fuels we use contain just carbon & hyrdrogen (hydrocarbons)
  1. Biofuels
    1. renewable energy sources like plants & waste
      1. only produce carbon dioxide & water when burnt
    2. said to be carbon neutral
    3. electric batteries can be used. have no exhaust gases
      1. electricity made by burning fossil fuels so doesn't remove pollution
2. many hydrocarbons are fossil fuels formed from the remains of dead plants & animals over millions of years
3. drilled out of the earth & refined
complete combustion-
1. hydrocarbon + oxygen -> carbon dioxide + water
carbon monoxide
1. only one oxygen atom attached to one carbon atom
2. produced if not enough oxygen present when fuels burn- incomplete combustion
3. very poisonous- displaces oxygen levels in the body by attaching to haemoglobin & starving vital organs of oxygen
  1. can lead to death
particulates
1. usually small particles of carbon
  1. deposits as soot, can affect some breathing issues
sulphur based air pollution
1. fuels contain impurities
  1. some contain sulphur
    1. when sulphur burns with oxygen- makes sulphur dioxide
      1. stays in atmosphere
        leaves as acid rain- dilute sulphuric acid
        affects the environment, lakes become acidic killing animals & plants
nitrogen based air pollution
1. nitrogen in the air produces nitrogen monoxide & dioxide
  1. pollutants or cause acid rain
reducing pollution
1. reduce electricity use. less fossil fuels needed to be burnt in power stations the less pollution there is
  1. sulphur can be removed from gas and oil used in power stations making little sulphur dioxide
  2. sulphur dioxide can be removed from flue gases by reacting with an alkali- called wet scrubbing.
  3. to reduce CO2, reduce amount of fossil fuels burnt.
catalytic converters
1. convert harmful nitrogen monoxide into harmless nitrogen and oxygen. This is a reduction reaction
  1. convert carbon monoxide into carbon dioxide by adding oxygen (oxidation reaction)
    1. cars tested every year by MOTs

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chemistry module one

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