7.1 Carbon components as fuels & feedstock

Question 1

What is crude oil?

Answer 1

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.

Question 2

What is a hydrocarbon?

Answer 2

A compound made up exclusively of hydrogen and carbon atoms

Question 3

What are alkanes?

Answer 3

Saturated hydrocarbons of a general formula:
CnH2n+2

Question 4

What is a homologous
series?

Answer 4

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

Question 5

Describe the combustion of
hydrocarbons

Answer 5

● 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.

Question 6

Describe the physical
properties of alkanes

Answer 6

● 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.

Question 7

Explain how fractional
distillation of crude oil takes
place

Answer 7

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

Question 8

What is cracking?

Answer 8

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

Question 9

What type of reaction is
cracking?

Answer 9

Thermal decomposition

Question 10

What are the conditions for
cracking?

Answer 10

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)

Question 11

How are the products of
cracking used?

Answer 11

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

Question 12

What is an alkene?

Answer 12

Unsaturated hydrocarbon. Contains a C=C bond.

General formula for alkenes is:
CnH2n