C9 - Crude Oil and Fuels Flashcards
What is a hydrocarbon?
A compound made up of Hydrogen and Carbon atoms ONLY.
What are alkanes?
Saturated hydrocarbons of a general formula Cn
H2n+2
Describe the combustion of hydrocarbons.
- Exothermic reaction occurring when hydrocarbons are reacted with oxygen.
- Complete combustion produces carbon dioxide and water (carbon and hydrogen atoms are completely oxidised).
- Incomplete combustion produces carbon and/or carbon monoxide and water.
Describe the physical properties of alkanes.
- 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.
Explain how fractional distillation of crude oil takes place.
- Crude oil is heated and vaporised.
- Vapour 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.
What is cracking?
When large hydrocarbons are broken down by the action of heat into smaller and more useful hydrocarbon molecules.
What are the conditions for cracking?
Reactant heated to vapour, passed over a hot catalyst (catalytic cracking)
OR
heated to vapour, mixed with steam and heated to high temperatures (steam cracking).
How are the products of cracking used?
The products are smaller alkanes and
alkenes – used as polymers and starting materials
for synthesis.
What is an alkene?
Unsaturated hydrocarbon. Contains a C=C bond.
General formula for alkenes is: CnH2n
What is the test for alkenes?
Add bromine water. Colour change occurs from orange to colourless.
