Energy from Fuels (Cambridge (CIE) IGCSE Physics): Revision Note

Fossil fuels

• Fossil fuels are:

  • Coal

  • Natural gas (mostly methane)

  • Crude oil which is refined into petrol, diesel and other fuels

Fossil fuels: coal, oil and natural gas

• Fossil fuels are formed from the remains of plants and animals 

• Chemical energy stored in fossil fuels originally came from sunlight

  • Energy from the Sun was transferred to the chemical energy store of plants by photosynthesis (plants use energy from sunlight to make food)

  • Animals ate the plants and the energy was transferred to their chemical store

Advantages of fossil fuels

• Fossil fuel power stations are extremely reliable since they can burn fossil fuels on demand and the infrastructure is well established in most countries

  • Energy output is not dependent on weather conditions

• Fossil fuel power stations are extremely responsive (they can be turned on and off easily), which means they can meet the changing demands of a nation

• Fossil fuels are relatively safe to store and use

Disadvantages of fossil fuels

• It takes millions of years for fossil fuels to form

  • This is why they are considered to be a non-renewable energy resource

  • The increasing demand for a decreasing supply causes prices to increase

  • Fossil fuels are being used far faster than they form, so supplies are finite and will become increasingly difficult and expensive to extract.

• Burning fossil fuels pollutes the atmosphere with harmful gases such as:

  • Carbon dioxide which contributes to the greenhouse effect

  • Sulfur dioxide which produces acid rain

  • Both carbon dioxide and sulfur dioxide can be captured upon burning, preventing them from being released into the atmosphere but this is expensive to do

• Extraction of fossil fuels causes damage to the environment

Uses of fossil fuels

• Fossil fuels are used for:

  • Transport

  • Generating electricity

  • Heating

Transport

• The majority of vehicles in the world are powered by petroleum products such as petrol, diesel and kerosene

  • These resources all originate from crude oil, which is a fossil fuel

• A growing number of vehicles are now being powered by electricity

  • The advantage of this is that while the vehicle is being driven, it produces zero carbon emissions

  • The disadvantage is that when the vehicle is being charged, it is connected to the electricity grid, which currently uses a combination of renewable and non-renewable energy sources

Electricity generation

• Fossil fuels, such as gas and coal, are used to produce energy on-demand when energy is needed

  • The fossil fuel is burned (combusted) and used to heat water to produce steam

  • The steam turns a turbine

  • The turbine turns a generator, which generates electricity

  • The current produced is transmitted via the electricity grid

  • The steam is condensed into water to be used again

Electricity generation in a coal-fired power station

Fossil fuels are burned to heat water to produce steam. The steam turns the turbine, which turns the generator, which produces electricity

• Electricity plays a bigger role in people's lives than ever before

  • With almost 8 billion people in the world, this means the demand for electricity is extremely high

  • To keep up with this demand, a combination of all the energy resources available is needed

Global energy consumption

In 2019, fossil fuels supplied around 80% of the world's primary energy. Burning them raises the level of carbon dioxide in the atmosphere, which contributes to global warming

Heating

• The majority of heating systems run on fossil fuels

  • Gas central heating systems are the most common, with a gas boiler that heats water through a system of pipes and radiators throughout the building

  • Boilers can also be powered by oil or biofuels

  • Open fireplaces burn wood or coal

• Electric heaters run on electricity

• Bottled gas can also be used in portable heaters

  • Bottled gas is either propane or butane which are also produced from fossil fuels

Biofuels

• Biofuels are made from plant matter

  • Energy from sunlight is transferred to the chemical store of plants

• Ethanol or methane can be produced and used in place of fossil fuels

  • However, they have only half the energy density of fossil fuels

Plants take in carbon dioxide during photosynthesis, but carbon dioxide is released back into the atmosphere when biofuels are burned

Advantages of biofuel

• Biofuel is a renewable resource since new plants can always be grown

• Biofuels provide a reliable and consistent supply of energy because the fuel can be stored and burned in a boiler whenever the electricity is needed

• Biofuel is generally considered to be carbon neutral

  • Although burning biofuels releases carbon dioxide into the atmosphere, the plants used to make the fuel take in carbon dioxide when they photosynthesise

• No sulfur dioxide is produced, so biofuels do not contribute to acid rain

• Some vehicles can be powered by biofuel rather than using fossil fuels

• Biofuel is added to petrol and diesel products in many countries to reduce the volume of pollutants released in combustion 

Disadvantages of biofuel

• Crops of biofuel-producing plants must be grown, which takes time

  • Growing the crops takes a lot of land, and takes resources needed for food production

• Burning biofuels releases carbon dioxide into the atmosphere

  • If the land had been used to grow crops for food, the same amount of carbon would have been taken out of the atmosphere, and much less carbon would have been returned

• Biofuels have only half the energy density of fossil fuels, which means twice as much fuel needs to be used to release the same amount of energy

• Not many vehicles can run on biofuel alone

Nuclear fuel

• Energy stored in the nucleus of atoms can be released when the nucleus is broken in two

  • This is known as nuclear fission (opens in a new tab)

Nuclear Fission: when a large nucleus is broken into two smaller nuclei, energy is released

• Nuclear power stations use fission reactions to heat water to produce steam, to turn turbines that turn generators which generate electricity

Advantages of nuclear power

• Nuclear power stations do not emit carbon dioxide or sulfur dioxide during operation, so they do not contribute to global warming or acid rain

• Nuclear power stations are extremely reliable since nuclear fuel can be used on demand and stations are well established in some countries

• Nuclear power stations are responsive as the output is easily controlled

• Nuclear fuel has a high energy density

  • A small amount of fuel releases massive amounts of energy

Disadvantages of nuclear power

• Nuclear power is a non-renewable resource

  • Uranium ore is mined from rocks so there is a finite supply

• Nuclear fuels produce radioactive waste

  • Radioactive waste is packaged and buried underground to be stored for thousands of years

  • Burial sites must remain undisturbed and uninhabited

• There are severe environmental consequences and risks of mutations or cancer if there is a radioactive leak, meaning heavy containment is necessary

• Nuclear power stations are extremely expensive to build and to decommission (close down)

• There is a high cost associated with maintaining safe storage facilities for the radioactive waste