Alkanes

Question 1

What is the purpose of vacuum distillation?

Answer 1

1. Allows heavier fractions to be further separated without high temperatures which could break them down

Question 2

What is a vacuum distillation unit?

Answer 2

1. Heavy residuals from the fractioning column are distilled again under a vacuum
2. Lowering the pressure over a liquid will lower its boiling point

Question 3

What is cracking?

Answer 3

1. Conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds

Question 4

What are the economic reasons for cracking?

Answer 4

1. Shorter chain more in demand
2. Products of cracking are more valuable then the starting materials

Question 5

What is fractional distillation in terms of IMF

Answer 5

The splitting of weak van der waals forces between molecules

Question 6

What are the conditions for thermal cracking?

Answer 6

High pressure (7000 kPa)
High temperature (400-900 Celsius)

Question 7

What are the products of thermal cracking?

Answer 7

1. Produces mostly alkenes
2. Sometimes produces hydrogen

Question 8

What are the conditions for catalytic cracking?

Answer 8

Slight or moderate pressure
High temperature (450 degrees)
Zeolite catalyst

Question 9

What are the products of catalytic cracking?

Answer 9

Produces branched and cyclic alkanes
Aromatic hydrocarbons

Question 10

What are the advantages of catalytic cracking?

Answer 10

1. Branched and cyclic hydrocarbons burn more cleanly and are used to give fuels a higher octane number
2. Cheaper than thermal cracking because it saves energy as lower temperatures and pressures are used

Question 11

What is a fuel?

Answer 11

Releases energy when burnt

Question 12

What are the products of complete combustion?

Answer 12

CARBON DIOXIDE AND WATER

Question 13

What are the products of incomplete combustion?

Answer 13

Carbon monoxide and carbon particulates

Question 14

How is acid rain formed?

Answer 14

1. Sulfur containing impurities produce SO2 when burned
2. SO2 will dissolve in atmospheric water

Question 15

How can sulfur dioxide be removed?

Answer 15

1. Flue gas desulfurisation
2. Acidic sulfur dioxide reacts with calcium oxide in a neutralisation reaction

Question 16

How is the strong nitrogen bond broken?

Answer 16

1. High temperature and spark in the engine provides sufficient energy

Question 17

What are catalytic converters made of?

Answer 17

1. Ceramic honeycomb
2. Coated with a thin layer of platinum, palladium & rhodium
3. Gives large surface area

Question 18

What do catalytic converters do?

Answer 18

Remove carbon monoxide, nitrogen oxides and unburned hydrocarbons to turn them into ‘harmless’ carbon dioxide, nitrogen and water

Question 19

What are the 3 steps of the free radical substitution mechanism?

Answer 19

1. Initiation
2. Propagation
3. Termination

Question 20

What are free radicals?

Answer 20

A reactive species which has an unpaired electron