Combustion of Fossil Fuels

When fossil fuels undergo combustion (burning) they release energy. This is useful for things like heating our homes, powering our cars, and generating electricity. However, the combustion of fossil fuels also creates pollution and contributes to global warming.

There are two types of combustion that can take place with hydrocarbons: complete and incomplete.

Complete Combustion

Most fuels contain carbon and hydrogen, and during combustion, they react with oxygen.

  • The hydrogen atoms are oxidised to form water (H2O)
  • The carbon atoms are fully oxidised to carbon dioxide (CO2)

This type of combustion, where all the fuel burns and fully reacts with oxygen, is called complete combustion. During the complete combustion of hydrocarbon fuels, only carbon dioxide and water are produced. Therefore, if carbon dioxide forms, we can tell that complete combustion has taken place.

diagram on a light blue background depicts the combustion of hydrocarbons. Vibrant flames rise from a row of hydrocarbon molecules, symbolised as 'CH'. Arrows indicate oxygen molecules, labelled 'O2', feeding the fire. As a result of the combustion, the diagram shows the release of carbon dioxide and water vapour, represented by 'CO2' and 'H2O' symbols, respectively. The entire process is summarised below the flames: 'HydroCarbon (CH) + Oxygen (O2) leads to Carbon Dioxide (CO2) + Water (H2O)'. The representation shows the chemical transformation during burning.

  • Complete combustion produces a lot of energy and is the ideal way to burn fossil fuels

For example, let’s look at the combustion of methane, a hydrocarbon found in natural gas:

Methane + Oxygen → Carbon dioxide + Water

CH4 + 2O2CO2 + 2H2O

As you can see, the carbon and hydrogen atoms in methane combine with oxygen to form carbon dioxide and water. However, there needs to be enough oxygen present for complete combustion to take place.

Incomplete Combustion

Incomplete combustion is another process that can occur when hydrocarbons burn. This process takes place when there isn’t enough oxygen available for complete combustion to occur. Incomplete combustion forms carbon monoxide (CO) and water.

Methane + Oxygen → Carbon monoxide + Water

2CH+ 3O22CO + 4H2O

However, incomplete combustion can also produce particulate carbon, also known as soot.

Methane + Oxygen → Carbon + Water

CH+ O2C + 2H2O

Carbon monoxide and soot

Carbon monoxide is a colourless, odourless and tasteless gas, which makes it quite hard to detect. It is very toxic and often called the “silent killer”. However, it can be detected by carbon monoxide detectors.

When we inhale carbon monoxide, it binds to haemoglobin in the blood. This reduces the oxygen carrying capacity of red blood cells in our body.

An illustrative diagram details the harmful effects of carbon monoxide inhalation in the human body. On the left, a human figure breathes in a mixture of carbon monoxide (CO) and oxygen (O2) molecules. The central section shows a magnified view of blood vessels, where carbon monoxide enters the bloodstream and binds with haemoglobin. This is contrasted against the normal process of oxygenation, depicted on the right. The final section emphasises the danger: as the body replaces the oxygen in red blood cells with carbon monoxide, it can lead to grave tissue damage and become life-threatening.

If the cells around the body do not get a sufficient amount of oxygen, this can cause death.

Soot is made up of small carbon particles and is produced when hydrocarbons are burned incompletely. Soot can cause respiratory problems when inhaled, and it can also contribute to global dimming.

  • Global dimming is a reduction in solar energy that reaches the Earth’s surface

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