8.1: Fuels

What are fossil fuels?

Fuels formed from the remains of ancient organisms over millions of years under heat and pressure.

Name three main fossil fuels.

Coal, crude oil, and natural gas.

What is crude oil?

A finite mixture of hydrocarbons found in the Earth's crust.

What are hydrocarbons?

Compounds made only of hydrogen and carbon atoms.

What is the general formula for alkanes?

CnH2n+2

What is an alkane?

A saturated hydrocarbon containing only single bonds.

Are alkanes saturated or unsaturated?

Saturated — they only contain single covalent bonds between carbon atoms.

What is the name of the process used to separate crude oil?

Fractional distillation.

Why is crude oil separated by fractional distillation?

Because it is a mixture of hydrocarbons with different boiling points.

How does fractional distillation work?

Crude oil is heated, and the vapours rise up the fractionating column, condensing at different heights depending on their boiling points.

Do longer-chain hydrocarbons have higher or lower boiling points?

Higher boiling points.

What trend is seen in boiling point with increasing hydrocarbon chain length?

Boiling point increases with chain length.

What trend is seen in viscosity with increasing hydrocarbon chain length?

Viscosity increases — longer chains are thicker and flow less easily.

What trend is seen in flammability with increasing hydrocarbon chain length?

Flammability decreases — longer chains burn less easily.

What trend is seen in cleanliness of flame with increasing chain length?

Shorter chains burn with a cleaner flame; longer chains with a smokier flame.

What is complete combustion?

When a hydrocarbon burns in plenty of oxygen to produce carbon dioxide and water.

What is the word equation for complete combustion of a hydrocarbon?

Hydrocarbon + oxygen → carbon dioxide + water

What are the products of complete combustion?

Carbon dioxide and water.

What is incomplete combustion?

When a hydrocarbon burns in a limited supply of oxygen, producing carbon monoxide or carbon and water.

What are the possible products of incomplete combustion?

Carbon monoxide (CO), carbon (soot), and water.

Why is carbon monoxide dangerous?

It is a toxic gas that binds to haemoglobin and prevents oxygen transport in the blood.

Why is soot (carbon) a problem?

It causes respiratory problems and blackens buildings.

Why are fossil fuels considered non-renewable?

They take millions of years to form and are being used faster than they are replaced.