C.2 Fossil fuels - core

Essential idea:

The energy of fossil fuels originates from solar energy which has been stored by chemical processes over time. These abundant resources are non-renewable but provide large amounts of energy due to the nature of chemical bonds in hydrocarbons.

Nature of science:

Scientific community and collaboration-the use of fossil fuels has had a key role in the development of science and technology. (4.1)


Fossil fuels were formed by the reduction of biological compounds that contain carbon, hydrogen, nitrogen, sulfur and oxygen.

Petroleum is a complex mixture of hydrocarbons that can be split into different component parts called fractions by fractional distillation.

Crude oil needs to be refined before use. The different fractions are separated by a physical process in fractional distillation.

The tendency of a fuel to auto-ignite, which leads to "knocking" in a car engine, is related to molecular structure and measured by the octane number.

The performance of hydrocarbons as fuels is improved by the cracking and catalytic reforming reactions.

Coal gasification and liquefaction are chemical processes that convert coal to gaseous and liquid hydrocarbons.

A carbon footprint is the total amount of greenhouse gases produced during human activities. It is generally expressed in equivalent tons of carbon dioxide.

Applications and skills:

Discussion of the effect of chain length and chain branching on the octane number.

Discussion of the reforming and cracking reactions of hydrocarbons and explanation how these processes improve the octane number.

Deduction of equations for cracking and reforming reactions, coal gasification and liquefaction.

Discussion of the advantages and disadvantages of the different fossil fuels.

Identification of the various fractions of petroleum, their relative volatility and their uses.

Calculations of the carbon dioxide added to the atmosphere, when different fuels burn and determination of carbon footprints for different activities.


The cost of production and availability (reserves) of fossil fuels and their impact on the environment should be considered.