These are detailed Revision Notes for Topic Nine (Chemistry of the Atmosphere) of AQA GCSE Chemistry. They are written by me, using a combination of class notes, text books and revision guides. I have also uploaded the other chapters in my store.
Chemistry of the
Atmosphere
The Early Atmosphere:
The Earth was formed about 4.6 million years ago, the Earth was a hot
ball of molten rock, made of interstellar dust and rock. It is the remains
of dead stars. There was no atmosphere because all the gases boiled
off into space. Then the earth cooled to form a crust.
After Volcanoes erupted and produced molten lava, carbon dioxide,
methane, steam and ammonia. Then earth cooled below 100°C and so
water began to condense and it rained for a long, long time to create
all the oceans. Most of the carbon dioxide and all the ammonia,
dissolved into the oceans
3 billion years ago, photosynthesis by marine organisms absorbed
most of the CO₂. This reduced the greenhouse effect, lowering the
temperature of the earth. The photosynthesis produced oxygen. Which
rises into the upper atmosphere and absorbs ultra violet radiation from
the sun to form ozone O₃. Ozone continues to absorb ultra violet
radiation and allows life to develop outside of the oceans.
Large amount of CO₂ was trapped in shells and then was deposited to
form Limestone. Photosynthesis by carboniferous forests trap large
amounts of carbon dioxide. The trees die, become buried in mud, then
fossilised into coal seams.
Now things are balanced though the equations of photosynthesis and
respiration. As photosynthesis is 6 C O2 +6 H 2 0→ C 6 H 12 O6 + 60₂ and
respiration is C 6 H 12 O6 + 6O2 →6 C O2+6 H 2 O. The Atmosphere now is made
up of 78% Nitrogen, 21% Oxygen, 0.9% Argon, 0.037% Carbon Dioxide
and the rest is made up of other gases like Water Vapour, Helium,
Methane and Hydrogen.
Greenhouse Gases:
Greenhouse gases like carbon dioxide, methane and water vapour act
like an insulating layer in the Earth’s atmosphere this is what allows
the Earth to be warm enough to support life.
All particles absorb certain frequencies of radiation. Greenhouse gases
don’t absorb the incoming short wavelength radiation from the sun- but
they do absorb the long wavelength radiation that gets reflected
towards the earth. The longwave radiation is thermal radiation, so it
results in warming of the surface of the Earth. This is the greenhouse
effect.
Some form of human activity affects the amounts of greenhouse gases
in the atmosphere
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