Alkanes

Crude oil is:

-the fossilised remains of dead plankton formed over millions of years

-found in porous rock in the Earth's crust

-a finite resource that is used to produce fuels and other chemicals

Hydrocarbons mostly make up crude oil. They vary in size and this affects their properties and how they can be used as fuels

The larger the hydrocarbon:

-the more viscous it is

-the higher its boiling point

-the less volatile it is

-the less easily it ignites

Fractional distillation can be used to separate crude oil into different parts

Each part(fraction) contains hydrocarbons with a similar number of carbon atoms. Most of them are alkanes

Method: Firstly, the crude oil is heated until it evaporates

The vapour then moves up the fractioning column which is much colder at the top than at the bottom

Shorter hydrocarbons condense and are collected at the top of the fractioning column

Longer hydrocarbons condense at higher temperatures and are collected lower down the column

Varying lengths of hydrocarbons condense at different points depending on their point of condensation

Carbon atoms are linked to four other atoms by single bonds

Alkanes are described as saturated as they only have single bonds

They are fairly unreactive but burn well

General formula for alkanes: C(n)H(n+2)

Drawing alkanes with single lines between atoms represents single covalent bonds

The shorter chain alkanes release energy more quickly by burning so there is a larger demand for them as fuels

Most fuels are compounds of hydrogen and carbon and many also contain sulfur

During the combustion of hydrocarbon fuels:

-both carbon and hydrogen are oxidised

-energy is released

-waste products are produced and released into the atmosphere

If combustion is incomplete, carbon monoxide, unburnt fuels and solid particles containing soot may be released

Carbon monoxide is a colourless, odourless, toxic gas

Particulates can cause global dimming by reducing the amount of sunlight reaching the Earth's surface and can cause damage to people's lungs

Due to the high temperatures reached when fuels burn, nitrogen in the air can react with oxygen to form nitrous oxides which can cause respiratory problems in people and react with rainwater to form acid rain which can damage plants and buildings

Sulfur can be removed from fuels before burning and be removed from waste gases after combustion