7.1 Carbon components as fuels & feedstock

Crude oil is a mixture of compounds; a fossil fuel consisting of the remains of ancient biomass. Finite resource - cannot be replaced as it is used up.

A compound made up exclusively of hydrogen and carbon atoms

Saturated hydrocarbons of a general formula: CnH2n+2

Series of compounds with same general formula, same functional groups and similar chemical properties.

● Exothermic reaction occurs when hydrocarbons are reacted with oxygen. ● Complete combustion produces carbon dioxide and water (carbon and hydrogen atoms are completely oxidised). ● Incomplete combustion produces carbon or carbon monoxide and water.

● First few in series are gases, then change to liquids, then to solids. ● In general, boiling points and viscosity increase as molecules get bigger. ● Volatility and flammability decrease as molecules get bigger. ● Poor reactivity.

• Crude oil is heated and vaporised. • Vapor rises up the fractionating column (tower). • The column is hotter at the bottom and cooler at the top. • Hydrocarbons cool as they go up the column and condense at different heights, as they have different boiling points. • Large molecules, high boiling points - collected at the bottom. • Small molecules, low boiling points - collected at the top. • This gives fractions, which can be used in various ways.

When large hydrocarbons are thermally broken down into smaller and more useful molecules

Thermal decomposition

Reactant heated to vapor, passed over a hot catalyst (catalytic cracking) or heated to vapor, mixed with steam and heated to high temperatures (steam cracking)

The products are alkanes and alkenes – used as polymers and starting materials for synthesis.

Unsaturated hydrocarbon. Contains a C=C bond. General formula for alkenes is: CnH2n