3.3.2 Alkanes

Question 1

Are alkanes saturated or unsaturated

Answer 1

Saturated

Question 2

Thermal cracking
Condition + products

Answer 2

• high pressure and temperature
• lots of alkenes - used to make polymers

Question 3

Catalytic cracking
Catalyst, conditions & products

Answer 3

• Zeolite catalyst
• slight pressure & high temperature
• aromatic hydrocarbons and alkanes

Question 4

Complete combustion is when

Answer 4

There is sufficient supply of oxygen

Question 5

Products of complete combustion

Answer 5

Water and co2

Question 6

Incomplete combustion is when

Answer 6

There is a limited supply of oxygen

Question 7

Products of incomplete combustion

Answer 7

Carbon monoxide (CO) and water

Question 8

Why is carbon monoxide bad

Answer 8

Toxic
Binds to haemoglobin so prevents oxygen being carried round the body

Question 9

Why is soot bad

Answer 9

Causes respiratory issues

Question 10

How are nitrogen oxides formed

Answer 10

High pressure & temperature cause the nitrogen and oxygen atoms in the air to react together
Nitrogen monoxide

Question 11

Reaction between carbon monoxide and nitrogen monoxide

Answer 11

2CO + 2NO —> 2CO2 +N2

Question 12

What are the 3 pollutants from a cars exhaust

Answer 12

Nitrogen oxides
Unburnt hydrocarbons
Carbon monoxide

Question 13

Reactions of a catalytic converter to remove the 3 pollutants from a cars exhaust
2 things to remember

Answer 13

1) complete combustion of a hydrocarbon
E.g. C3H8 +5O2 —> 3CO2 + 4H2O
2) 2NO —-> N2 + O2
3) 2NO + 2CO —> N2 + 2CO2

Include state symbols
All of them are gases

Question 14

What are the 3 steps of free radical substitution

Answer 14

Initiation step
Propagation step
Termination step

Question 15

What is needed for free radical substitution to occur

Answer 15

Ultra violet light

Question 16

Are alkanes reactive or in reactive + why x2

Answer 16

Unreactive

Non polar (carbon + hydrogen similar electronegativity)
Bonds are relatively strong (lots of energy to break)

Question 17

What is a free radical

Answer 17

Any species with an unpaired electron

Question 18

This is the initiation step
Cl-Cl—> *Cl + *Cl
But what is the name for this reaction of the bond breaking

Answer 18

Homolytic Fission

Question 19

What would you do to prevent further substitution

Answer 19

Use an excess of the alkane E.g. methane
To prevent further substitution

Question 20

Cracking produces …

Answer 20

An Alkene and alkane

Question 21

Formula of soot

Answer 21

C

Question 22

Why is soot bad for car

Answer 22

Builds up in the engines so car does not work properly

Question 23

Why is sulphur dioxide bad

Answer 23

Causes acid rain

Question 24

How is the issue of sulfur dioxide resolved

Answer 24

The sulfur dioxide is removed from flue gases by wet srubbing
An alkali E.g. calcium carbonate is used to neutralise the sulfur dioxide

Question 25

Explain why XYZ does not lead to depletion of ozone layer

Answer 25

Does not release Cl radicals