Summary AQA GCSE Chemistry - Chemistry of the Atmosphere (Topic 9)
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Course
Science
Institution
GCSE
Detailed notes summarising C9, Chemistry of the Atmosphere for anyone studying GCSE AQA 9-1 Chemistry. Written by me, and are a good revision tool that covers all points of the specification in this topic. There are hand drawn diagrams, detailed summaries of harder concepts and also a few practice ...
C9 – Chemistry of the Atmosphere
9.1 – Composition and Evolution of the Atmosphere
What was the early atmosphere like?
Primarily made up of carbon dioxide, with virtually no oxygen, this is similar to the
atmosphere of the planets Mars and Venus today. The evidence for this is in the fossil
record, which shows gases conserved which scientists can study.
Why was it like this?
Scientists have different theories, the most heavily accepted one is that the first billion years
of the Earth’s history consisted of intense volcanic activity which released large quantities of
the gases carbon dioxide and water vapour, as well as smaller amounts of ammonia,
methane, hydrogen and nitrogen from the inside of the Earth.
What is the atmosphere like today?
Today’s atmosphere is mainly
Gases in today's atmosphere compromised of nitrogen, which
takes up 78% of Earth’s modern
atmosphere. Other gases also
include:
Nitrogen Oxygen Argon
Carbon Dioxide Other gases
other gases (such as neon, helium, methane, water vapour)
How did the amount of oxygen in the atmosphere increase/carbon dioxide decrease?
Primitive algae and plants developed, and with the plentiful supply of carbon dioxide they
began the process of photosynthesis. Photosynthesis stores carbon and water, turning it
into glucose, and more importantly: oxygen.
Photosynthesis –
Carbon dioxide + water glucose + oxygen
(you need to know this balanced
6CO2 + 6H2O → C6H12O6 + 6O2 equation)
, Through this process, the amount of oxygen began to steadily increase until more plant life
could flourish and grow, whilst carbon dioxide levels decreased, as the formation of the
oceans meant that the soluble gas dissolved readily into the oceans, to form soluble carbon
compounds – these were then precipitated as sedimentary rock. Later, these would be
used as fossil fuels.
9.2 – Carbon dioxide and methane as greenhouse gases
What are greenhouse gases?
Greenhouse gases are vital in the atmosphere to maintain temperatures on Earth, keeping
them high enough for life to survive.
Some of the key greenhouse gases include carbon dioxide, methane and water vapour.
What is the greenhouse effect and how does it work?
A naturally occurring process that acts as an insulating layer in the Earth’s atmosphere.
Short wavelength electromagnetic radiation is emitted from the Sun and passes through the
Earth’s atmosphere. Greenhouse gases do not absorb this short length radiation, but when the
incoming radiation hits the Earth, some is absorbed, but some is reflected as long wavelength
radiation. This can be absorbed by greenhouse gases, which then re-radiate it in all directions,
including back towards the Earth as thermal radiation, resulting in the warming of the surface of
the Earth.
To summarise this:
Greenhouse gases DO NOT absorb short length radiation from the Sun, only the long
wavelength radiation that has been reflected off the Earth.
Long wavelength radiation is thermal radiation, greenhouse gases re-radiating this results
in the warming of the surface of the Earth.
What is the enhanced greenhouse effect?
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