Fossil Fuels
Section: 11. Organic Chemistry | Syllabus: Cambridge AS Level Physics 9702
Fossil Fuels Fossil fuels are natural fuels formed from the remains of living organisms that died millions of years ago. They are our main source of energy but are non-renewable resources. Fossil Fuel A natural fuel formed from the remains of dead organisms (plants and animals) that have been subjected to high pressure and temperature over millions of years.
Main Types of Fossil Fuels Coal - formed from dead plant material in swamps and forests Crude oil (petroleum) - formed from dead marine organisms Natural gas - often found with crude oil deposits Formation of Fossil Fuels Fossil fuels form over millions of years through a complex geological process involving dead organisms, sediment, pressure, and heat.
Formation Process Dead organisms fall to the bottom of seas, lakes, or swamps They are covered by layers of sediment (sand, mud, rocks) High pressure and temperature over millions of years convert the organic matter into fossil fuels This process occurs in the absence of oxygen (anaerobic conditions) Key Point The formation of fossil fuels takes millions of years, which is why they are considered non-renewable resources - we cannot replace them in our lifetime.
Crude Oil and Hydrocarbons Crude oil is one of the most important fossil fuels and is the source of many useful products. Hydrocarbon A compound containing only carbon and hydrogen atoms. Crude oil is a complex mixture of different hydrocarbons.
Crude oil is a thick, black, sticky liquid Contains hundreds of different hydrocarbon compounds Also contains small amounts of sulfur, nitrogen, and oxygen compounds Must be separated into useful fractions before use Fractional Distillation of Crude Oil Crude oil is separated into useful fractions using fractional distillation, a physical separation method based on differences in boiling points.
Fractional Distillation A separation technique that separates a mixture of liquids with different boiling points by heating and condensing at different temperatures. The Distillation Process Crude oil is heated to about 350°C to vaporize most of it The vapor rises up a fractionating column which is hotter at the bottom and cooler at the top Different hydrocarbons condense at different heights depending on their boiling points Hydrocarbons with similar boiling points condense together as fractions Each fraction is collected at different levels Fractions from Crude Oil The fractionating column separates crude oil into several useful fractions, each with specific properties and uses.
Main Fractions (from top to bottom of column) Fraction Number of Carbon Atoms Boiling Point Range Uses Refinery gases C1 - C4 Below 40°C Bottled gas (camping gas), heating Gasoline (petrol) C5 - C10 40°C - 110°C Fuel for cars Naphtha C7 - C14 110°C - 180°C Chemical feedstock, making other chemicals Kerosene (paraffin) C10 - C16 180°C - 220°C Aircraft fuel, heating Diesel oil (gas oil) C15 - C20 220°C - 250°C Fuel for diesel engines, heating Fuel oil C20 - C30 250°C - 300°C Fuel for ships, power stations Lubricating oil C30 - C40 300°C - 350°C Lubricants, waxes, polishes Bitumen C40+ Above 350°C (residue) Road surfacing, roofing Trends in Fractions As the number of carbon atoms increases down the fractionating column: Boiling point increases - larger molecules have stronger intermolecular forces Viscosity increases - the liquid becomes thicker and flows less easily Flammability decreases - larger molecules are harder to ignite Color darkens - fractions become darker in color Important The fractions collected at the top of the column (refinery gases, petrol) have smaller molecules with weaker intermolecular forces, so they have lower boiling points and condense at cooler temperatures.
Uses of Fossil Fuels Fossil fuels are essential to modern society and have a wide range of applications. Fuel for transportation - petrol, diesel, kerosene for cars, trucks, planes, ships Heating - natural gas and fuel oil for homes and buildings Electricity generation - burned in power stations to produce electricity Raw materials - petrochemicals for making plastics, medicines, dyes, detergents Environmental Problems with Fossil Fuels The combustion of fossil fuels produces several harmful pollutants that damage the environment and human health.
Pollutants from Combustion Carbon dioxide (CO₂) - complete combustion produces CO₂, a greenhouse gas contributing to climate change and global warming Carbon monoxide (CO) - incomplete combustion produces toxic CO which can be fatal Sulfur dioxide (SO₂) - sulfur impurities in fuels burn to produce SO₂, which causes acid rain Nitrogen oxides (NOₓ) - high temperatures in engines cause nitrogen and oxygen from air to react, producing NOₓ which contributes to acid rain and photochemical smog Particulates (soot) - incomplete combustion produces carbon particles causing respiratory problems and global dimming Resource Depletion Issues Non-renewable - fossil fuels take millions of years to form, so they will eventually r…
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