Organic - 3.2 Alkanes

Question 1

What is a catalytic converter?

Answer 1

A device fitted in a car to reduce the amount of emissions from an internal combustion engine.

Question 2

Define catalytic cracking

Answer 2

A type of cracking that takes place at a slight pressure, high temperature and in the presence of a zeolite catalyst and is used mainly to produce motor fuels and aromatic hydrocarbons.

Question 3

Define cracking

Answer 3

A process which involves breaking C-C bonds in alkanes to produce shorter chained alkanes and alkenes.

Question 4

Define fractional distillation

Answer 4

A method of separating mixture of substances according to the different boiling points. Common used to separate crude oil into different fractions.

Question 5

Define hydrocarbons

Answer 5

Compounds made up of carbon and hydrogen atoms only

Question 6

Define saturated

Answer 6

Organic compounds are saturated if all the carbon-carbon bonds are single C-C bonds. Alkanes are saturated hydrocarbons.

Question 7

What is thermal cracking?

Answer 7

A type of cracking that takes place a high pressure and high temperature and produces a high percentage of alkenes.

Question 8

What is the general formula of alkanes?

Answer 8

CnH2n+2

Question 9

State the first four alkanes

Answer 9

Methane ethane propane butane

Question 10

Are alkanes polar and why?

Answer 10

No, because the difference in electronegativity between the carbon atom and hydrogen atom is very small

Question 11

How are mixtures of alkanes separated?

Answer 11

Through fractional distillation

Question 12

What is fractional distillation?

Answer 12

The continual evaporation and condensation of a mixture causing the components to separate because of a difference in their boiling points

Question 13

What is a fraction?

Answer 13

A group of compounds that have similar boiling points and are removed at the same level of a fractionating column

Question 14

Is a fractionating column hotter at the top or bottom?

Answer 14

Hot at the bottom and cool at the top

Question 15

What is cracking?

Answer 15

A process where long chain hydrocarbon molecules are broken into shorter chain molecules that are in high demand

Question 16

What happens in thermal cracking?

Answer 16

Long chain alkanes are heated to a very high temperature high-pressure and in a short time this produces shorter alkanes and rich in alkenes.

Question 17

What happens in catalytic cracking?

Answer 17

Long chain alkanes are heated under pressure with a zeolite catalyst

Question 18

What are the conditions and products of thermal cracking?

Answer 18

Temperature = 1000-1200K
Pressure = 700atm
Time = one sec
Catalyst = none
Products = high percentage of alkanes and short chain alkanes

Question 19

What are the conditions and products of catalytic cracking?

Answer 19

Temperature = 800-1000 K
Pressure = 1-2atm
Time = 2-4secs
catalyst = zeolite
Products = aromatic hydrocarbons and motor fuels

Question 20

Describe the complete combustion of alkanes

Answer 20

Alkanes burn in oxygen to produce carbon dioxide and water only

Question 21

Describe the incomplete combustion of alkanes

Answer 21

Alkanes will burn for water and carbon monoxide, which is toxic

Question 22

What is a catalytic converter?

Answer 22

Reduces the amount of carbon monoxide and nitrous oxide and unburnt hydrocarbons by converting them into less toxic gases

Question 23

Describe the process that occurs in an internal combustion engine

Answer 23

A small amount of fuel and excess air enters the combustion chamber.
The mixture is then compressed and ignited with a temperature spark .
Mixture then burns explosively forcing movement of the engine.
The products exit via the exhaust

Question 24

Why can sulphur dioxide be removed from flue gases by calcium oxide and calcium carbonate?

Answer 24

They neutralise the acidic sulphur oxide to form calcium sulphate which is used for construction

Question 25

What happens in the initiation step of the reaction between methane and chlorine?

Answer 25

The molecules of chlorine absorbed energy supplied by UV light and the chlorine covalent bond breaks.
Each atom from the bond leaves with one electron from the shared pair of electrons.
Two chlorine atoms are formed and each atom has an unpaired electron in the outer shell, these are called free radicals are are extremely reactive.

Cl2 -> Cl• + Cl•

Question 26

What happens in the propagation step of the reaction between methane and chlorine?

Answer 26

The highly reactive chlorine free radicals react with the methane molecules forming hydrogen chloride gas and a methyl free radical.
The meatball free radical reacts with a second chlorine molecule forming chloromethane and another chlorine free radical .
Discontinuing process of producing free radicals is known as a chain reaction .

Cl• + CH4 -> HCl + •CH3
•CH3 + Cl2 -> CH3Cl + Cl•

Question 27

What happens in a termination step of the reaction between methane and chlorine?

Answer 27

In order for the reaction to stop to the radicals must collide and react for a molecule.

Cl• + Cl• -> Cl2
Cl• + •CH3 -> CH3Cl
•CH3 + •CH3 -> C2H6

Question 28

What is the reaction between methane and chlorine called?

Answer 28

A free radical substitution reaction

Question 29

What is the process called that involves the breaking of a covalent bond to produce two free radicals?

Answer 29

Homolytic fission