(4.11-4.18) Hydrocarbon combustion + Cracking

What is a fuel?

A substance that releases heat energy when burned

What are the products of complete hydrocarbon combustion?

carbon dioxide + water

What is incomplete combustion?

The burning of a substance without sufficient oxygen.

What are the products of incomplete combustion?

Usually:

CO2, H20, CO, C

Why is carbon monoxide so dangerous?

It binds irreversibly with haemoglobin in the blood

decreasing its capacity to transport oxygen

Why does burning some hydrocarbons result in sulphur dioxide?

Fossil fuels contain some sulphur impurities.

When combusted, that sulphur reacts with oxygen,

producing sulphur dioxide.

Why do petrol engines produce oxides of nitrogen?

the temperature reached is high enough

to allow nitrogen and oxygen in the air to react

forming oxides of nitrogen.

How does sulphur dioxide and oxides of nitrogen contribute to acid rain?

The O2/H20 in the air

react with sulphur dioxide

to produce sulfuric acid or sulfurous acid.

Nitrogen oxides produce nitric acid.

These acids mix with water and fall to the ground as acid rain.

Why is acid rain dangerous?

Acidifies bodies of water- killing animals/plants

Why are longer chain hydrocarbons split?

Demand for shorter chains is higher than longer chain hydrocarbons

How are longer chain hydrocarbons split?

Catalytic cracking-

producing petrol, paraffin and ethene (polymers)

What is catalytic cracking?

• form of thermal decomposition

• vapourised hydrocarbons

  • at (600-700 degrees)

• passed over powdered catalyst

  • silica or alumina

• producing shorter chain hydrocarbons