Petroleum: Definition, Formation, Refining and Uses

Petroleum is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. It is a crucial natural resource that powers industries, homes, and vehicles and is a key raw material in manufacturing diverse everyday products.

What is Petroleum in Chemistry?

A petroleum refers to a naturally occurring, complex mixture of hydrocarbons found deep within the Earth’s crust. This concept appears in chapters related to hydrocarbons, fossil fuels, and organic compounds, making it a foundational part of your chemistry syllabus. 

Petroleum is most commonly found in liquid form (crude oil) but is also present as natural gas and solid forms like bitumen. It is also called "black gold" due to its immense value and utility in producing fuels, chemicals, and materials.

Molecular Formula and Composition

The molecular formula of petroleum cannot be written as a single compound because it is a mixture. It consists mainly of hydrocarbons: alkanes (paraffins), cycloalkanes (naphthenes), and aromatic hydrocarbons. 

By weight, petroleum is about 80–87% carbon and 10–15% hydrogen, along with small quantities of sulfur, nitrogen, oxygen, and trace metals. It is categorized under mixtures of hydrocarbons.

Preparation and Synthesis Methods

In nature, petroleum forms over millions of years through the decomposition of ancient marine organisms. Their remains are buried under layers of sediment, exposed to heat and pressure, and gradually converted into crude oil and natural gas. 

Industrially, petroleum is extracted by drilling wells deep into underground rock reservoirs. It is pumped up as crude oil and then sent to refineries for processing.

Physical Properties of Petroleum

Petroleum is usually a thick, dark-colored liquid with a characteristic smell. Its boiling point range is wide because it is a mixture, not a pure substance. Crude oil can range from light (watery) to heavy (thick and viscous). It is less dense than water, floats on water, does not dissolve in water, and is flammable.

Chemical Properties and Reactions

• Petroleum's hydrocarbons undergo combustion with oxygen to release energy, forming carbon dioxide and water. 
• Some fractions can be cracked to smaller molecules (cracking), hydrogenated (adding hydrogen), or used as starting blocks in making chemicals like plastics.
• Presence of sulfur or nitrogen causes pollution on burning, which can be controlled during refining.

Frequent Related Errors

• Confusing petroleum with pure chemical compounds (it is a complex mixture, not one compound).
• Assuming all fractions are the same (different fractions have different properties and uses).
• Mixing up coal and petroleum, though both are fossil fuels, their origin and composition differ.
• Forgetting petroleum can be both liquid (oil) and gas (natural gas).

Uses of Petroleum in Real Life

Petroleum is widely used in daily life. The most common uses include:

• Petrol (gasoline) and diesel: Fuels for vehicles.
• Kerosene: Jet fuel and household use.
• LPG (liquefied petroleum gas): Cooking and heating.
• Lubricants: Reduce friction in machinery.
• Paraffin wax: Candles, polishes, and crayons.
• Bitumen: Road construction.
• Petrochemicals: Source of plastics, synthetic fibers, detergents, fertilizers, and pharmaceuticals.

Relation with Other Chemistry Concepts

Petroleum is closely related to topics such as Hydrocarbons and Fossil Fuels, helping students build a conceptual bridge between energy sources, organic chemistry, and industrial applications. 

Understanding petroleum also also connects to the principles of Fractional Distillation, as this is the primary method used to separate crude oil into useful products.

Step-by-Step Reaction Example

Let's see how fractional distillation separates petroleum components:

1. Crude oil is heated in a furnace.

2. The vapors enter a tall fractionating column that is hotter at the bottom, cooler at the top.

3. As the vapors rise, they cool, and components condense at different levels based on boiling points.

4. Lower boiling fractions (like LPG, petrol) condense near the top; higher boiling fractions (like diesel, lubricating oil, bitumen) condense lower down.

5. Each fraction is collected and processed further for various uses.

Lab or Experimental Tips

Remember fractional distillation by the rule of "top is cooler—light fractions rise, bottom is hotter—heavy fractions stay." Vedantu educators often highlight this in live classes to help you visualize and remember the process, especially using diagrams of the refinery column.

Try This Yourself

• List two products you use daily that come from petroleum.
• Explain why petroleum is called "black gold."
• Draw a labeled diagram of a fractionating column.
• Give one environmental effect of burning petroleum fuels.

Final Wrap-Up

We explored petroleum—its natural formation, chemical composition, refining process, and real-life uses. This knowledge is key for understanding not just chemistry but also its impact on industry, environment, and everyday life. For more detailed explanations and exam-prep tips, explore live classes and topic notes on Vedantu.

Hydrocarbons
Fractional Distillation
Synthetic Polymers