Alkanes

Question 1

General formula

Answer 1

CnH2n+2

Question 2

Is there a double bond?

Answer 2

No

Question 3

Fractional distillation process

Answer 3

• preheated oil passes into fractionating column
• temperature decreases upwards
• lower boiling point molecules condense higher up the column

Question 4

Why do smaller alkanes have lower boiling points

Answer 4

As they have fewer and weaker LDF between molecules

Question 5

What condenses higher and lower in the column

Answer 5

Petrol and gasoline condense higher up
Diesel and bitumen condense lower down

Question 6

Cracking
- process
- what it does

Answer 6

Done by passing long hydrocarbon through a heated catalyst (Zeolite)
Large molecules break up into smaller ones

Question 7

Reforming
What it does
How
Benefits

Answer 7

Used to convert straight-chain alkanes into branched-chain alkanes and cyclical hydrocarbons
Helps fuels burn smoother
Heat them with a catalyst (usually platinum)

Question 8

Complete combustion equation

Answer 8

Alkane + oxygen —> carbon dioxide + water

Question 9

Problems pollutants made by incomplete combustion cause
- Solid Carbon

Answer 9

Smoke or soot can be harmful when inhaled
Global dimming

Question 10

Problems pollutants made by incomplete combustion cause
- carbon monoxide

Answer 10

Toxic gas causes death by binding with the iron in haemoglobin rather than oxygen

Question 11

Problems pollutants made by incomplete combustion cause
- unburnt hydrocarbons

Answer 11

A small proportion released causing global warming

Question 12

Problems pollutants made by incomplete combustion cause
- oxides of sulfur

Answer 12

Acidic oxide when dissolved in water
Can form sulphuric acid leading to acid rain which damages forests, lakes and limestone buildings

Question 13

Problems pollutants made by incomplete combustion cause
- oxides of nitrogen

Answer 13

Produced by high temperatures in the engine
When dissolved in water it can produce nitric acid leading to acid rain

Question 14

Catalytic converters

Answer 14

Platinum
3-way catalysts removed CO, unturned hydrocarbon and oxides of nitrogen
2NO + 2CO —> N2 + 2CO2

Question 15

Alternative fuels
Biodiesel

Answer 15

Vegetable oils obtained from rapeseed and sunflowers

Question 16

Alternative fuels
Bio alcohol

Answer 16

Bio ethanol
Ethanol is produced by the fermentation of sugars and then separated from large amounts of water

Question 17

Positives and negatives of biofuels

Answer 17

Positives:
No exploration or drilling costs
Much closer to being carbon neural

Negatives:
Lots of land needed
Low yield
Substations costs in growing
Processing and transport

Question 18

Positives and negatives of natural gas

Answer 18

Positives:
No land needed
Very high yield
Processing and transport costs are low

Negatives:
Exploration and drilling costs are high
Not carbon neutral

Question 19

Radical definiton

Answer 19

A species that contains an unpaired electron

Question 20

Substitution reactions of alkanes
Named example and condition

Answer 20

Halogenation (chlorination)
Occurs when the mixture is exposed to UV light

Question 21

Name the 3 stages of halogenation substitution reaction of alkanes

Answer 21

• Initiation
• Propagation
• Termination

Question 22

Describe initiation reaction
For chlorine and methane

Answer 22

UV radiation breaks the chlorine molecule into 2 chlorine atoms
Each chlorine atom takes one electron from the shared pair - homolytic fission
They are both radicals

Question 23

Describe propagation reactions for methane and chlorine

Answer 23

Chlorine radicals are very reactive so remove a hydrogen atom from the methane molecule
Methyl radical is formed which is very reactive
It reacts with other chlorine molecules

Question 24

What are propagation reactions

Answer 24

Where radicals and molecules collide to produce radicals and molecules

Question 25

Describe termination reactions for chlorine and methane

Answer 25

Combination of reactions occur
A radical and a radical collide to form a molecule

Question 26

Initiation equation for chlorine and methane

Answer 26

Cl2 —> Cl* + Cl*

Question 27

2x propagation reaction equations for methane and chlorine

Answer 27

Cl* + CH4 —> HCl + CH3*
CH3* + Cl2 —> CH3Cl + Cl*

Question 28

3x termination equations for methane and chlorine

Answer 28

Cl* + Cl* —> Cl2
Cl* + CH3* —> CH3Cl
CH3* + CH3* —> C2H6