crude oil + hydrocarbons

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 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 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.
• Boiling points and viscosity increase as molecules get bigger.
• Volatility and flammability decrease as molecules get bigger.
• Poor reactivity.
• long chain hydrocarbons are very viscous

Question 7

Explain how fractional
distillation of crude oil takes
place

Answer 7

• Crude oil is heated and vaporised.
• Vapor rises up the fractionating column
• 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.

Question 8

What is cracking?

Answer 8

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

Question 9

What type of reaction is

cracking?

Answer 9

Thermal decomposition

Question 10

What are the conditions for

cracking?

Answer 10

catalytic cracking - high temperature and catalyst
- reactant heated to vapour, passed over a hot catalyst

steam cracking - high temperature and steam
- hydrocarbon heated to vapour, then mixed with steam and heated to high temperatures

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 viscosity? what does it mean if something has a high viscosity?

Answer 12

the thickness of a fluid, if it has a high viscosity it is thick and flow slowly.

Question 13

what happens during the combustion of hydrocarbons?

Answer 13

hydrocarbons release energy when burned. Carbon and hydrogen in fuel react w/ oxygen, get oxidised. if the oxygen isnt limited, produces co2 and water (complete combustion)

Question 14

why are alkenes useful?

Answer 14

used to make polymers
starting material for other materials
more reactive than alkanes