Fuels Revision

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C1-Chemistry in Our World
Topic5- Fuels
Fuels are chemicals which give us energy when burnt.
We use mainly fossil fuels: crude oil, coal and natural gas
These are non-renewable.
Renewable fuels: biofuels, hydrogen
Crude oil:
This is a mixture of hydrocarbons.
Hydrocarbons are compounds of hydrogen and carbon ONLY.
To make use of crude oil, the mixture needs to be fractionally distilled and the individual
components have specific uses.
How is crude oil formed:
6 mark question -The energy in fossil fuels originated from the sun. Describe how the sun's
energy came to be incorporated in crude oil.
1. Microscopic plants in the sea get their energy from the sun by photosynthesis
2. The animals that live in the sea feed on these plants.
3. When they die the fall to the bottom of the sea.
4. They become buried by sediments that fall to the bottom of the sea
5. These sediments prevent oxygen from getting to the dead animals so they do not rot
6. Heat and pressure turn them into crude oil- this take millions of years.
7. Because the oil is less dense than water, it will float on water and move up through porous
rocks.
8. It gets trapped when it gets to a layer of rocks that is non-porous[caprock]- so cannot move
further.
9. The oil remains there until pipes are drilled through the rocks to remove it.
Natural gas is made in the same way but from remains of plants.
Fractional Distillation:
3- 4 mark question.
Explain how petrol is obtained from crude oil.
1. Crude oil is heated up to about 400°C
2. The vapours are then fed into the fractionating column which has shelves maintained at
various temperatures.
3. There the vapours travel upwards
4. Each fraction condenses at a temperature just below its boiling point and is collected.
5. Petrol will be collected near the top because it has a short chain.
Summary:
Fraction Length of Ease of Boiling point Viscosity Uses
molecule ignition
Gases Short ­ up Easy Low < 0°C Runny-low Fuel for cars {LPG}
to 4 C Camping gas
Cooking and heating
homes {methane}
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Petrol Fuel for cars
Kerosene Fuel for aircrafts
Diesel Fuel for vehicles ­
lorries, cars etc
Fuel oil Fuel for large ships
and some power
stations
Fuel for heating
Lubricating oil
Bitumen Long- up to Difficult High >350°C Thick - Road surfacing
40 C high Waterproofing flat
roofs
Combustion: this is a reaction of fuels with oxygen ­ it is oxidation.
Complete= when there is excess oxygen
Only products: water and carbon dioxide plus energy
More efficient ­ little energy wasted.…read more

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Products of combustion
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Problems with burning:
1. Soot- causes lung disease if breathed in
2. Carbon monoxide- this is a toxic gas and reduces the amount of oxygen transported in the
blood- it kills in a very short time
3. Carbon dioxide ­ causes global warming- the cloud of carbon dioxide prevent the reflected
rays of the sun from leaving the Earth making the temperatures abnormally high.
4.…read more

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This is mixed with normal diesel
Advantages:
1. Carbon neutral ­ the carbon in the fuels originally came from plants so the CO2 that is
released goes back into the plants for photosynthesis.
2. They are renewable- plants can grow quickly
Disadvantages:
The processing of the fuels uses fossil fuels.
Hydrogen powered fuel cells:
1. Formed by electrolysis of water or from natural gas
2. Advantages- only product is water ­ no CO2 produced,
Disadvantages:
1.…read more

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