Open in App
Log In Start studying!

Select your language

Suggested languages for you:
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|
Crude Oil

Crude oil was formed over many millions of years, with the oldest deposits estimated to be around 500 million years old and the youngest approximately 50 years. While it may not be immediately apparent from looking at crude oil, it was all, in fact, once living organisms.Crude oil significantly impacts…

Content verified by subject matter experts
Free StudySmarter App with over 20 million students
Mockup Schule

Explore our app and discover over 50 million learning materials for free.

Crude Oil

Illustration

Lerne mit deinen Freunden und bleibe auf dem richtigen Kurs mit deinen persönlichen Lernstatistiken

Jetzt kostenlos anmelden

Nie wieder prokastinieren mit unseren Lernerinnerungen.

Jetzt kostenlos anmelden
Illustration

Crude oil was formed over many millions of years, with the oldest deposits estimated to be around 500 million years old and the youngest approximately 50 years. While it may not be immediately apparent from looking at crude oil, it was all, in fact, once living organisms.

Crude oil significantly impacts society, underpinning virtually everything we do. Without it, we would not have transport, plastics, and many domestic products. Its use is not without its issues, however, as it is responsible for many conflicts around the world and vast amounts of emissions contributing to global warming.

We'll learn the definition of crude oil, its formation and composition, the types that exist, an overview of crude oil distillation, and the products made from it.

The Definition of Crude Oil

It is referred to as crude oil, as when it is extracted from the underground geological formations in which it is found, it contains a mixture of hydrocarbons, all with different lengths, properties and uses. Before they can be used, these hydrocarbons need to be separated from one another in a process known as refining.

Crude oil is a liquid mixture of relatively volatile hydrocarbons of varying lengths.

Crude Oil Petroleum, a type of crude oil StudySmarterFig. 1. A beaker and flask containing samples of petrol, which is obtained from crude oil.

The crude oil industry, and its many products, are referred to as the petrochemical industry. Crude oil acts as the primary feedstock of hydrocarbons used in industry, with refined petroleum products used in everything from plastic to skincare to fuels.

The Formation of Crude Oil

When ancient organisms died, they gradually fell to the bottom of the sea or ocean. Here, they mixed with the sediment found at the bottom, slowly building into a deeper and deeper layer. This layer underwent anaerobic decomposition, which meant the bodies were only partially decomposed. Over time, further layers build up on top of this seam of partially broken-down organic matter, compressing it.

A popular misconception about crude oil is that it is formed from dinosaurs. While the image of us pottering about in vehicles powered by the remains of what was once such magnificent animals is quite evocative, it is unfortunately not true. Crude oil is predominantly formed from tiny marine plankton and algae remains.

The sediment eventually compacts into rock kilometres thick, which then exerts massive pressure on the seam of organic matter. This pressure, along with the high temperatures under kilometres of rock, causes the organic matter to convert into oil, along with shattering the vein of rock above the oil into shale. This shale allows the oil to travel up before its passage upwards is blocked by the next layer of impermeable rock, a reservoir rock. We then drill into this layer when extracting oil for use.

Crude Oil Distillation of crude oil at an oil rig StudySmarterFig. 2. An example of the oil rigs used to extract oil via offshore drilling.

It is important to remember that while an area may not be currently underwater, the world has undergone drastic changes over millions of years, so what is now land may once have been underwater.

This is how we can find oil and gas underground rather than just under the sea.

An example of this transition from underwater to land is that of the Himalayas. Despite now being well above sea level, the rock which makes up much of this mountain range was once underwater in an ancient sea known as the Tethys sea. This sea eventually dried up and receded, leaving the Himalayas hundreds of miles from the nearest ocean. However, fossilised remnants of the ancient sea's inhabitants were left behind and now appear within the mountain range.

The length of time required for the layer of organic material to build up and be converted into oil makes crude oil a non-renewable resource. While more may eventually form, this would be over such a long timescale that for practical human use, it is effectively finite.

Difference Between Crude and Refined Oil

Refined oil has had all the impurities that could cause harm removed. It is more suitable for human use. It is also easier to store than crude oil as crude oil is easily oxidised and deteriorated. Crude oil is refined to meet set standards.

The Composition of Crude Oil

As discussed in the above definition section, crude oil is a complex mixture of relatively volatile hydrocarbons with varying lengths.

As the name suggests, hydrocarbons are molecules comprised solely of hydrogen and carbon.

The carbon generally forms a backbone of varying shapes and configurations, with the hydrogens bonded to them. The ability to create this backbone stems from carbon atoms' ability to form 4 covalent bonds.

These bonds underpin organic chemistry, with the ability of carbon to start families of similar compounds, known as homologous series, which may contain chains or rings of carbon atoms.

Hydrocarbons generally exist in one of 4 states: gases, liquids, low melting or polymerised solids. Hydrogens can be classified using many methods; however, the two main ones are by whether they are fully saturated with hydrogen or not and by the types of bonds present.

Saturated VS Unsaturated Hydrocarbons

Saturated hydrocarbons have the maximum possible number of hydrogen atoms bonded to each carbon. They include only single bonds in the carbon backbone. This backbone may be a straight or branched line of carbons or contain one or more rings.

When classifying hydrocarbons by the bonds present, these are known as alkanes.

On the other hand, unsaturated hydrocarbons contain one or more double or triple bonds between carbons. This means that at least two carbons are bound to less than the maximum number of carbons. Like saturated hydrocarbons, these can have straight, branched or ring-containing structures.

When classifying by bond types, those with double bonds are called alkenes, whereas those with triple bonds are known as alkynes.

If a hydrocarbon contains an aromatic ring, then the hydrocarbon is known as an aromatic hydrocarbon.

Alkenes are hydrocarbons containing at least one carbon-to-carbon double bond. The double bond also enhances their reactivity, which is why these are generally not common in crude oil. The general formula of alkenes is CnH2n.

If you are interested, please read up on the IUPAC naming of alkenes

Alkynes are hydrocarbons containing at least one carbon-to-carbon triple bond. As a homologous series, Alkynes do not have a general formula, but simple examples with only one triple bond can be represented by the formula CnH2n-2.

This means that alkenes and alkynes are unsaturated, as the extra bond takes up a space that could be used for hydrogen.

Alkanes

Alkanes, as discussed above, are hydrocarbons containing only single bonds with no other functional groups. They have a general formula of CnH2n+2, where n is the number of carbon atoms within the molecule and is saturated with hydrogen, meaning each carbon is bound to the maximum possible number.

General Formula - A chemical formula which reflects the formula of an entire class of compounds, such as the homologous series alkanes.

The formula of each alkane differs by CH2 from those on either side of it in the homologous series. The physical properties of the alkanes gradually change as you go along the series, an example of which is the boiling point increasing progressively as the chains get longer.

The fractions produced when crude oil is refined using fractional distillation largely contain mixtures of members of this homologous series.

The naming of alkanes is relatively simplistic, with family members always ending in the -ane suffix.

Alkanes are generally named for the number of carbons contained within their structure. If the fact that it is a straight vs branched chain is vital to their properties, then the prefix n- is added to the name of the straight chain alkane to distinguish it from the branched equivalent.

Some examples of alkanes are:

FormulaName
CH4Methane
C2H6Ethane
C3H8Propane
C4H10Butane
C5H12Pentane
C6H14Hexane

When an alkane has five or more carbon atoms, the naming uses the appropriate numerical prefix, such as penta-, drops the a from the end and adds the suffix ane.

An eight-carbon alkane, for example, would use the prefix octa-. We remove the a from the end to give us oct, then add the -ane suffix to leave us with octane, which you may recognise from its addition in varying amounts to fuels for cars.

Types of Crude Oil

There are four main types of crude oil and this affects fractional distillation which is explained further below.

  • Very light oils: these fuels are very volatile and include:
    • Gasoline
    • Kerosene
    • Jet fuel
  • Light Oils: these are moderately volatile and of medium toxicity. They include:
    • Most domestic fuel oils
    • Diesel fuel oils
  • Medium Oils: these oils are the most common and have a higher viscosity and a lower volatility in comparison to light oils.
  • Heavy fuel oils: these are the most toxic of crude oils as well as the most viscous and least volatile.
    • They include heavy marine fuels.

Viscosity refers to how easily the oil flows. For example: honey is more viscous than water.

Volatility refers to how easy the oil evaporates. A substance that is a gas at room temperature is highly volatile.

Crude Oil Distillation

As crude oil is a mixture of many different compounds, all with varying chemical and physical properties, these must generally be separated for any of the individual components to be used, generally through a process known as fractional distillation. These refined products can then be manipulated further by modifying their structures. One way this is being done is through cracking.

Crude Oil Distillation of crude oil at an oil refinery StudySmarterFig. 3. An oil refinery in Kuwait, processing crude oil into useful end products such as petrol and diesel.

As discussed in the alkane section, members of a homologous series exhibit a gradual change in physical properties as you progress along the series. This includes boiling point, and this gradual variation allows us to use fractional distillation to separate the mixture that is crude oil into its component compounds.

The crude oil is heated at the base of a large tower, with several condensers at varying heights. The heating causes many components of the crude oil to vaporise and begin to move up the tower. As they rise, they gradually cool. By knowing the temperature at which each desired fraction condenses and the rate at which the vapours cool, we can position condensers to condense and collect each fraction.

Longer hydrocarbons have a higher boiling point and therefore condense first, meaning they are pulled off lower down the tower. The shorter a hydrocarbon is, the lower its boiling point, and the further it will move up the tower before condensing.

For a more in-depth look at fractional distillation, look at our full-length article on the subject!

Cracking

The varying fractions we can extract from crude oil have varying uses, from lubrication to gases to fuel stoves, etc. Because of these varying uses, there are differing levels of demand for each of the fractions. The ratio of the fractions extracted from crude oil does not always match this demand, meaning scientists needed to develop a way to manufacture more of specific fractions. They can do this by shortening, extending or otherwise modifying hydrocarbons.

Cracking is the technique scientists use to shorten hydrocarbons, creating more short-chain fractions.

For example, if the demand for petrol exceeds the need for the lubricating oils produced lower down the distillation tower, the long chains found within this fraction can be broken down, forming shorter chains, which can then be added to the petrol fraction, increasing the amount available for sale.

Cracking is a complex process with several methods, but each generally uses a catalyst and high temperatures.

The exact techniques used within the industry for cracking are explored in more depth in our full-length article on the subject.

Products Made From Crude Oil

Most derivatives of crude oil are used as fuel for diverse activities. Here is a list of the main products of fractional distillation and how we use them:

  • Liquid petroleum gases: fuel for domestic use (heating, cooking)
  • Petrol or gasoline: fuel for most cars
  • Naphta: chemicals and plastic manufacturing
  • Kerosene of paraffin: fuel for aircraft
  • Diesel: fuel for trains and some cars
  • Fuel oil: fuel for ships and power stations
  • Bitumen: for roads and roofs

Crude Oil - Key takeaways

  • Crude oil is a non-renewable resource produced over millions of years from the partially decomposed remains of ancient plankton and algae.

  • It is generally found within deep rock formations and extracted through drilling.

  • It is a complex mixture of different hydrocarbons, generally belonging to the homologous alkane series, which are saturated hydrocarbons containing only single bonds.

  • The different hydrocarbons have varying properties depending on their length, meaning they all have different uses. These are referred to as fractions and are extracted from the mixture in a process known as fractional distillation.

  • Hydrocarbon chains may also be shortened in a process known as cracking to produce more of the shorter chain fractions.


References

  1. Fig. 1. Petroleum sample (https://commons.wikimedia.org/wiki/File:Petroleum_sample.jpg) by Nefronus, CC0 Public domain
  2. Fig. 2. An oil rig offshore Vungtau (https://commons.wikimedia.org/wiki/File:An_oil_rig_offshore_Vungtau.jpg) by Genghiskhanviet, Public domain
  3. Fig. 3. Mina-Al-Ahmadi oil refinery night (https://commons.wikimedia.org/wiki/File:Mina-Al-Ahmadi_oil_refinery_night.jpg) by Grubb, Public domain

Frequently Asked Questions about Crude Oil

Crude oil is a liquid mixture of relatively volatile hydrocarbons of varying lengths, often found in large underground formations, formed from ancient decaying organic matter. 

It is called crude oil as it is a mixture of hydrocarbons of varying lengths, which is relatively useless on its own. Before it can be used it generally requires further processing, in a process known as refining, which separates the individual hydrocarbons, each of which has varying properties and therefore uses. 

Crude oil is made primarily of relatively volatile hydrocarbons of varying lengths. 

Crude oil is a non-renewable resource since it is formed over a long time period from the fossilised remains of ancient plants and animals. 

Crude oil and petroleum are not the same, however, these terms are often used interchangeably. Petroleum is a mixture that contains crude oil but also gases. Crude oil only contains liquid hydrocarbons. 

Final Crude Oil Quiz

Crude Oil Quiz - Teste dein Wissen

Question

What is chemical cracking?

Show answer

Answer

Chemical cracking is the process of breaking down large molecules into smaller, more useful ones.

Show question

Question

Which molecules do we typically crack in chemistry?

Show answer

Answer

Short-chain hydrocarbons

Show question

Question

Why do we crack longer-chain hydrocarbons?

Show answer

Answer

Longer-chain hydrocarbons aren't that useful to us and have a low demand. However, cracking longer-chain hydrocarbons produces shorter-chain hydrocarbons, which are more useful and have a higher demand. By turning longer-chain hydrocarbons into shorter-chain ones, we increase their economic value.

Show question

Question

Cracking longer-chain hydrocarbons produces ____ and ____.

Show answer

Answer

Short-chain alkanes

Show question

Question

Give two uses of short-chain alkanes.

Show answer

Answer

For example:


  • Fuel for cars.
  • Fuel for our homes.
  • Cigarette lighters.
  • Aerosols.

Show question

Question

Give two uses of alkenes.

Show answer

Answer

For example:


  • To make polymers like plastics.
  • As a chemical feedstock.
  • In solvents.
  • In medicines.
  • In paints.

Show question

Question

What are alkenes?

Show answer

Answer

Alkenes are unsaturated hydrocarbons that contain at least one C=C double bond.

Show question

Question

Cracking hydrocarbons involves breaking ____.

Show answer

Answer

A C-C single bond.

Show question

Question

Which type of hydrocarbon fraction is typically more useful to us?

Show answer

Answer

Longer-chain hydrocarbon fractions

Show question

Question

Describe the conditions and process of steam cracking.

Show answer

Answer

The hydrocarbons are vapourised, then mixed with steam and briefly heated to extremely high temperatures.

Show question

Question

Describe the conditions and process of catalytic cracking.

Show answer

Answer

The hydrocarbons are vapourised and passed over a hot catalyst.

Show question

Question

Steam cracking produces a high proportion of ____.

Show answer

Answer

Alkenes

Show question

Question

Catalytic cracking produces a high proportion of ____.

Show answer

Answer

Short-chain alkanes

Show question

Question

Why is crude oil known as crude oil?

Show answer

Answer

Because it consists of a mixture of hydrocarbons, which must be separated through refining before use, making it a crude resource. 

Show question

Question

What elements are found in hydrocarbons? 

Show answer

Answer

Carbon

Show question

Question

What is the definition of crude oil?

Show answer

Answer

Crude oil is a liquid mixture of relatively volatile hydrocarbons of varying lengths. It is known as crude oil as it must be refined through a process known as fractional distillation, which separates it into its component compounds, each with varying properties and therefore uses. 

Show question

Question

What is the name for the industry surrounding crude oil and the products created from it?

Show answer

Answer

The petrochemical industry.

Show question

Question

What timescale is crude oil created over? 

Show answer

Answer

Millions of years

Show question

Question

What organisms is oil created from?

Show answer

Answer

Marine plankton and algae

Show question

Question

Why do the algae and plankton not fully decompose at the bottom of the ocean? 

Show answer

Answer

The low oxygen conditions present at the bottom of the ocean mean they decayed through anaerobic decomposition, rather than aerobic. 

Show question

Question

What compressed the partially decomposed organisms, leading to the formation of oil? 

Show answer

Answer

The gradual building up of layers of sediment, which eventually form into sedimentary rock. 

Show question

Question

What layer of rock is drilled into to extract oil?

Show answer

Answer

Reservoir rock. 

Show question

Question

What lies just below the reservoir rock?

Show answer

Answer

Shale, which the oil is forced up into by the immense pressure and heat created by the heavy layer of rock above the reservoir. 

Show question

Question

What physical conditions convert the partially decomposed organisms into crude oil?

Show answer

Answer

Low oxygen, high heat and pressure caused by large amounts of rock 

Show question

Question

If oil is created at the bottom of oceans, how can it be found on land?

Show answer

Answer

Oil can be found on land as areas that are now not underwater may have once been. This is because the world has changed dramatically over the millions of years since the oil was formed. 

Show question

Question

What kind of rock contains oil?

Show answer

Answer

Sedimentary rock, as it is formed by the gradual accrual and then compression of many individual particles of sediment. 

Show question

Question

Is oil made from dinosaurs?

Show answer

Answer

No

Show question

Question

What is a saturated hydrocarbon?

Show answer

Answer

A hydrocarbon with each carbon bonded to as many hydrogen atoms as possible, meaning only single bonds are present between carbons. 

Show question

Question

What is a non-saturated hydrocarbon?

Show answer

Answer

A hydrocarbon in which double or triple carbon to carbon bonds exist, meaning not every carbon is bonded to the max possible number of hydrogen. 

Show question

Question

How many bonds may carbon form?

Show answer

Answer

4 covalent bonds

Show question

Question

What is a homologous series in the context of hydrocarbons? 

Show answer

Answer

A group of similar compounds which differ by CH2 in their structure from those adjacent in the series. They exhibit similar chemical properties, and a gradual change in physical properties as you move along the homologous series. 

Show question

Question

What type of carbon to carbon bonds exclusively make up the alkanes?

Show answer

Answer

Carbon to carbon single bonds. 

Show question

Question

What is the general formula for an alkane? 

Show answer

Answer

CnH2n+2

Show question

Question

What is the definition of a general formula? 

Show answer

Answer

A chemical formula which reflects the formula of an entire class of compounds, such as the homologous series alkanes. 

Show question

Question

What are the first four alkanes? 

Show answer

Answer

Methane, Ethane, Propane, Butane

Show question

Question

What is the chemical formula of methane?

Show answer

Answer

CH4

Show question

Question

What is the chemical formula of methane?

Show answer

Answer

CH4

Show question

Question

What is the chemical formula of ethane?

Show answer

Answer

C2H6

Show question

Question

What is the chemical formula of propane?

Show answer

Answer

C3H8

Show question

Question

What is the chemical formula of butane?

Show answer

Answer

C4H10

Show question

Question

Why must crude oil be processed before use?

Show answer

Answer

As it is a mix of hydrocarbons, all with differing properties, they must be separated from each other before each can be used for its specific use, dictated by its property. 

Show question

Question

How are crude oil fractions separated from one another?

Show answer

Answer

Fractional Distillation

Show question

Question

How does fractional distillation separate different hydrocarbons from the mix that is crude oil?

Show answer

Answer

 By heating oil at the base of a tower, with condensers at different heights, these can be pulled off. As hydrocarbons rise they cool, condensing on the relevant condenser. 

Show question

Question

Why are longer hydrocarbons pulled off lower down the fractional distillation column? 

Show answer

Answer

Their longer length means a higher boiling point. This means as they cool, they condense earlier and lower down the tower. 

Show question

Question

Why are short hydrocarbons pulled off nearer the top of the fractional distillation tower?

Show answer

Answer

Their shorter length means they have a lower boiling point, therefore remaining a vapour for longer and rising further up the tower before condensing. 

Show question

Question

What molecule makes up the backbone of hydrocarbons?

Show answer

Answer

Carbon

Show question

Question

Must the carbon backbone of hydrocarbons be straight?

Show answer

Answer

No, it can be branched or straight.

Show question

Question

Which has a lower boiling point?



Show answer

Answer

Short chain hydrocarbons 

Show question

Question

Which has a low viscosity?



Show answer

Answer

Short chain hydrocarbons 

Show question

Question

Which has a lower flammability?



Show answer

Answer

Long chain hydrocarbons 

Show question

Test your knowledge with multiple choice flashcards

Which molecules do we typically crack in chemistry?

Cracking longer-chain hydrocarbons produces ____ and ____.

Cracking hydrocarbons involves breaking ____.

Next

Flashcards in Crude Oil50+

Start learning

What is chemical cracking?

Chemical cracking is the process of breaking down large molecules into smaller, more useful ones.

Which molecules do we typically crack in chemistry?

Short-chain hydrocarbons

Why do we crack longer-chain hydrocarbons?

Longer-chain hydrocarbons aren't that useful to us and have a low demand. However, cracking longer-chain hydrocarbons produces shorter-chain hydrocarbons, which are more useful and have a higher demand. By turning longer-chain hydrocarbons into shorter-chain ones, we increase their economic value.

Cracking longer-chain hydrocarbons produces ____ and ____.

Short-chain alkanes

Give two uses of short-chain alkanes.

For example:


  • Fuel for cars.
  • Fuel for our homes.
  • Cigarette lighters.
  • Aerosols.

Give two uses of alkenes.

For example:


  • To make polymers like plastics.
  • As a chemical feedstock.
  • In solvents.
  • In medicines.
  • In paints.
More about Crude Oil

Join over 22 million students in learning with our StudySmarter App

The first learning app that truly has everything you need to ace your exams in one place

  • Flashcards & Quizzes
  • AI Study Assistant
  • Study Planner
  • Mock-Exams
  • Smart Note-Taking
Join over 22 million students in learning with our StudySmarter App Join over 22 million students in learning with our StudySmarter App

Discover the right content for your subjects

Sign up to highlight and take notes. It’s 100% free.

Start learning with StudySmarter, the only learning app you need.

Sign up now for free
Illustration