GCSE Chemistry - Crude Oil and Hydrocarbons: What is Crude Oil and How Do We Use It?

What is crude oil? What is it used for? How do you break crude oil into multiple fractions?

These are all questions that spring to mind when exploring how valuable crude oil is. It is important to understand that crude oil is one of the most valuable commodities in the world. Why?


Crude oil contributes extensively to global economic growth because crude oil has so many uses. This includes powering factories and vehicles or simply being traded across financial markets. However, crude oil is a finite resource; and questions emerge that because it is limited - why is everyone chasing it? 

The simple answer - crude oil is multifunctional. It is used for almost every vehicle on the planet and this allows the world to function. Be it commuting to work, travelling abroad or transporting goods and commodities all require crude oil. This article will explore in detail how crude oil is broken down and the uses involved.

  • The first section discusses what exactly crude oil is.
  • The second explores what crude oil is used for.
  • The third explores the benefits and issues with combustion and incomplete combustion.
  • Finally, thoughts will be provided towards alternatives to crude oil. 

A mix of Hydrogen (white) and Carbon Atoms (black).

What is Crude Oil?

Before crude oil can be discussed, we must apply some definitions. Firstly, crude oil is made up of hydrocarbons which are compounds made from hydrogen and carbon. Hydrocarbons are made up of a mixture of rings and chains; with carbon atoms being black and hydrogen atoms white.

Their properties and uses are determined by how many carbon atoms and hydrogen atoms there are in a molecule as well as how they are arranged.

Long chains of hydrocarbons act very differently from short circular chains. The variety of their properties makes them very useful in different fuel applications or as different types of plastics. In order to separate and create each type of hydrocarbon from crude oil - it must first be refined.

Fractional distillation is the process where crude oil is taken and vaporised into a distillation unit; which then rises and cools to form a liquid. A variety of liquids are created which is how different fuels are made.

Once these fuels have been created they need to be applied to an oxidant at a high temperature to produce a gaseous reaction through combustion. This is what produces power for human goods and services to function.

Fractional Distillation

Fractional distillation is the process where crude oil is vaporised, producing a variety of liquids. The liquids are separated into fractions; with heavier liquids towards the bottom and lighter liquids as you rise up the distillation unit. These separated products are the key to powering most of our goods and services. 

Fractions with Different Boiling Points

Uses of Crude Oil

Crude oil provides many uses; which is where the process of fractional distillation emerges. Fractional distillation breaks crude oil down into different fractions to power a huge number of goods and services. Combustion engines will be explored which look into what the process caused, including pollutants involved - but importantly, why the process is a necessity for human life.

On the other hand, incomplete combustion will be critiqued because of poisonous and carcinogenic gases being released which provide huge health and risk factors. Humanity is on the brink of an environmental crisis; so, a forward-looking approach needs to be conducted to provide better alternatives in order for humanity to survive. 

Petroleum Gas

Petroleum gas has the lowest boiling point of all other fuels and this is why it is at the top of the distiller. Petroleum gas is very flammable; making it a useful fuel. The common gas involved is propane which is frequently used for BBQs, domestic heating and use of cooking.

Propane has a boiling point of -42 degrees Celsius; illustrating why it is at the top of the distiller. When propane is mixed with oxygen, a chemical reaction occurs which creates an explosion of power. It is also important to note propane has the lowest viscosity out of all the other factions.

Viscosity is defined by how thick and sticky the liquid is. Propane is a gas and we can therefore understand why it has the lowest viscosity. 

Propane Gas being used for a Barbecue


Gasoline (Petrol)

Gasoline is one of the most bought commodities in the world. According to the U.S. Energy Information Administration, Americans used about 142 billion gallons of gasoline in 2019. It is a widespread commodity that has multiple uses including being the fuel for cars/light trucks, small aircraft, farming equipment and electricity generators.

For the average person; this is a highly bought fuel because many vehicles require it to travel. Firms including BP and Shell are some of the leading oil companies that produce, distribute and trade vast quantities of oil globally. 

Despite petrol being a frequently bought fuel, the world is gradually becoming greener with great attention being brought to the use of electric cars.


The process of petrol reacting with oxygen is known as combustion. When petrol mixes with oxygen, a chemical reaction forms which produces a lot of energy. In addition, petrol is a liquid and therefore it is more viscous than propane gas; though it still has a very low viscosity. The boiling point of petrol is around 94 degrees Celsius; though this can vary.


A Car Fuelling with Petrol



Kerosene (also known as Paraffin) is the main fuel used for jet aircraft. When wanting to travel by plane; the aircraft is filled with kerosene in order for flight to take place.

Kerosene is therefore one of the most bought fuels because of the large number of people that require planes to travel. To put the use of kerosene into context, a Boeing 747 burns around 4 litres of kerosene every second. If a plane is flying for 10 hours, it will burn roughly 150,000 litres of fuel.

The current UK price of kerosene is constantly changing because it is traded, but at this moment in time, it is 42 pence. Upon calculation, a 10-hour flight would cost that particular airline with a Boeing 747 around £63000.

Not only is the cost extortionate; but the toll on the environment is brutal. Most car fuel tanks are around 30 litres which can last a couple of weeks, and so in comparison to a plane, we can see the damage to the environment.

Finally, kerosene has a boiling point of around 200 degrees Celsius. This means it is further down the distiller unit towards the middle, as it has a higher boiling point than petrol but also any gases. 

An Aircraft that Requires Kerosene to Travel



Diesel is mainly used for some cars and trains. In the UK, around 42% of cars require diesel; though this number is falling at an alarming rate because of the UK government doing its best to prevent people buying diesel powered vehicles.

To support this, the UK government have banned the sale of petrol and diesel cars by 2030 to incentivise consumers to move to alternatives; like electric vehicles. In the UK, around 9.5 billion litres of diesel are used commercially every year illustrating its strong demand still in place. The boiling point of diesel is around 225 degrees Celsius. 

A Diesel Pump


Fuel Oil

Fuel oil is used as fuel for ships and to power some power stations. For example, a steam boiler in a station. The process works by fuel oil and oxygen mixing, which ignites a flame into tubes that are submerged underwater.

The heat from this combustion is sent to the tubes in the water. The heat makes the water evaporate which creates steam. The steam is transferred to certain pipes to be used for specific heating services. The process is additionally recyclable; where the steam can be taken after the process to be cooled and condensed back into water. The boiling point of fuel oil is around 275 degrees Celsius. 

A Ship that Requires Fuel Oil to Travel



Finally, bitumen is the most viscous fuel in fractional distillation. It is a very sticky liquid and forms right at the bottom of the distiller because it has the highest boiling point of 350 degrees Celsius or more.

Bitumen’s uses include surfacing down roads and roofs. For example, UK roads are notorious for potholes; and using bitumen provides a valuable function to fill these holes.

It is important to note that as you go down the distiller, the boiling points rise for the fuel, the viscosity increases because of the fuels being more sticky liquids and the ease of ignition worsens. For example, igniting petrol is far easier than fuel oil because it is a more flammable liquid. During the process of combustion ignites it much easier and releases more energy, more quickly.


Cracking is the process where large hydrocarbon molecules are broken down into smaller hydrocarbon molecules by heat and pressure. Cracking is one of the largest processes for the commercial production of common fuels like petrol and diesel.

Importantly, we need cracking because there isn’t enough petrol or diesel produced in the original process of fractional distillation. Simply put, we need a lot more petrol and diesel than crude oil initially makes through fractional distillation in order to meet global demand.

Fractional distillation of crude oil usually produces more long-chain hydrocarbons than short-chain hydrocarbons. As a result, we have an excess supply of larger hydrocarbons that are not needed. Cracking is used to break these larger hydrocarbons into smaller ones to produce fuels that are much more needed. 

Large Hydrocarbons Broken Down into Smaller Hydrocarbons



For a car or plane to move, we must use a propulsion system to power it. Combustion is the chemical process where fuel is mixed with oxygen and ignited, this ignition creates a chemical reaction. During the process of combustion, the chemical reaction creates carbon dioxide and water. Carbon dioxide is a notorious pollutant and greenhouse gas. Machines such as the combustion engine in cars are designed to transfer mechanical power (to turn the wheels of a car) from chemical energy stored in the fuel and released during combustion.

Combustion Engine Illustrating how Mechanical Power is Created from Fuel and Oxygen Mixing

Incomplete Combustion

Despite combustion being a highly used process; there are flaws. Incomplete combustion occurs when the supply of oxygen is poor. Water is still a product, but carbon monoxide and carbon and produced instead of carbon dioxide. The carbon is released as soot, which is a poisonous and odourless gas.

Carbon Monoxide behaves as a poisonous gas because it displaces oxygen in the blood which causes a deprivation of blood to the heart, brain and other vital organs. If a sufficient amount of oxygen is not delivered, in a matter of minutes the human body can suffocate; and potentially may cause death. Minor effects can include fatigue, dizziness and sudden chest pains.

Carbon Monoxide poisoning is most likely to deliver worse consequences in an indoor environment; because the toxic gas can loom in the air. For example, firefighters, mechanics and engine operators are most at risk. 

Carbon Monoxide is Produced by a Lack of Oxygen 


Alternatives to Petrol and Diesel

One of the latest innovations for powering vehicles is hydrogen fuel cells. They have been developed because hydrogen is an emission-free alternative compared to internal combustion engines which give off toxic and polluting gases. The only byproduct of hydrogen combustion is water.

One can understand the advantage hydrogen provides and the potential for the hydrogen market to expand.

Furthermore, refuelling hydrogen fuel cells only takes a few minutes; which delivers a competitive edge over electric cars whose batteries may take several hours to fully charge. The number of hydrogen vehicles is growing because of these great advantages; including 20 new hydrogen-powered buses in London, built to illustrate the efforts to crack down on pollution.

Airbus is also developing future technologies in the aviation industry to combat emissions by using hydrogen as a fuel.

Despite hydrogen appearing to be environmentally friendly and the answer to solving issues with toxic gases; there are a number of problems. Firstly, hydrogen fuel cells do not produce harmful gases but the actual production process to make hydrogen fuel does. Hydrogen is often produced from fossil fuels which is mainly specified towards natural gas.

Furthermore, factories working on fuel cells and the distribution of fuel cells globally all add to pollution in the air.

Secondly, hydrogen storage is very inefficient.

Compressive hydrogen requires about 13% of the total energy content of the hydrogen itself, and if hydrogen is turned into a liquid it loses about 40% of its total energy capacity. You could understand that storing hydrogen is inefficient, and gas being leaked is a large flaw in the process of creating hydrogen fuel cells. 

Hydrogen-powered Bus 


Final Recap

  • Fractional distillation is a vital process to allow vehicles and machinery to function. Without this process, humanity would be very limited in where it could travel or operate.

  • Crude oil is broken down into various fuels and as you go down the distiller, the fuels’ boiling point rises, as does the viscosity and number of hydrocarbons.

  • Although, larger hydrocarbons are more easily produced during distillation, and the process of cracking is used to break these large hydrocarbons down into smaller ones. 

  • Finally, once the fuels have been produced they are ready for use, combustion is where fuel and oxygen are mixed to provide power to vehicles.

  • This process creates carbon dioxide which adds to the large problem of global warming. Even worse, if there is a lack of oxygen, carbon monoxide is produced which may cause death.

  • Alternatively, the world is finding other means of producing non-polluting fuels like hydrogen but this is still very much in the early stages. 
Author's profile picture

Sebastian Owen

24th March

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