Chemistry Reference
In-Depth Information
Figure 6.6
Cutting coal today is extremely mechanised.
Figure 6.7
Oil production in the North Sea.
Over millions of years, as the layers of forming
coal were pushed deeper and the pressure and
temperature increased, the fi nal conversion to coal
took place (Figure 6.6). Different types of coal were
formed as a result of different pressures being applied
during its formation. For example, anthracite is a
hard coal with a high carbon content, typical of coal
produced at greater depths. Table 6.1 shows some
of the different types of coal along with their carbon
contents.
Table 6.1
The different coal types.
oil platform
North Sea
sea bed
non-porous rock
(cap-rock)
natural gas
pressure
Type of coal
Carbon content/%
Anthracite
90
oil
Bituminous coal
60
Figure 6.8
Natural gas and oil are trapped under non-porous rock.
Lignite
40
Peat
20
Oil and gas were formed during the same period
as coal. It is believed that oil and gas were formed
from the remains of plants, animals and bacteria that
once lived in seas and lakes. This material sank to the
bottom of these seas and lakes and became covered in
mud, sand and silt which thickened with time.
Anaerobic decay took place and, as the mud layers
built up, high temperatures and pressures were
created which converted the material slowly into oil
and gas. As rock formed, earth movements caused it
to buckle and split, and the oil and gas were trapped
in folds beneath layers of non-porous rock or cap-
rock (Figures 6.7 and 6.8).
Questions
1
Coal, oil and natural gas are all termed 'fossil fuels'. Why is
the word 'fossil' used in this context?
2 a
Name the process by which plants convert carbon
dioxide and water into glucose.
b
What conditions are necessary for this process to occur?
3
Draw a fl ow diagram to represent the formation of coal, oil
or gas.
