Alkanes

Question 1

What is an alkane?

Answer 1

A saturated hydrocarbons
containing C-H bonds only

Question 2

What is the general formula
of an alkane?

Answer 2

Cn H2n+2

Question 3

Are their bonds polar?
Why/why not?

Answer 3

Nonpolar- carbon and
hydrogen have similar
electronegativities

Question 4

Which intermolecular forces
do they have? Why?

Answer 4

Only van der Waals forces of
attraction - bonds are
non-polar

Question 5

Are they soluble in water?
why?

Answer 5

Insoluble because hydrogen bonds in
water are stronger than alkanes’ van der
Waals forces of attraction

Question 6

Which reactions will alkanes
undergo?

Answer 6

Combustion and reaction with
halogens

Question 7

What is crude oil? How is it
formed? Is it renewable?
Why?

Answer 7

Mixture of fractions (hydrocarbons with similar
boiling points and properties)
Formed at high temperatures and pressures deep
below earth’s surface over millions of years →
therefore non-renewable

Question 7

How reactive are alkanes?

Answer 7

Very unreactive

Question 8

Name the fractions from
high to low boiling point.

Answer 8

Gases - fuel on site
Gasoline/petrol/naphtha - cars
Kerosene/paraffin - jet fuel, lighting
Diesel oil - lorries/taxis
Lubricating oil/waxes - candles, engine oil
Fuel oil - ships, power stations
Tar/bitumen - roads/roofing
https://bit.ly/pmt-ed

Question 9

What is fractional
distillation/how does it
work?

Answer 9

Crude oil heated until mostly vapourised
Passed into a fractionating tower that is cooler at the top than the bottom
Liquid fractions are piped off at the bottom
Vapours rise up the column and - via trays and bubble caps - condense
when temperature < their boiling point
Shortest chain hydrocarbons condense at the top as they have the lowest
boiling points

Question 10

What is fracking and how is
it done?

Answer 10

Natural gas held within shale rock
Drill into shale, force pressurised water and sand into rock to
fracture it, Collect gas
HCl and methanol added to break up shale and prevent
corrosion

Question 11

Pros/cons of fracking?

Answer 11

Advantages - gas supply for many years, reduces imported
gas and electricity

Disadvantages - lots of traffic to local area, concern about
amount of water used, chemical additives can pollute water
supplies, can cause small earthquakes, combust CH4 → CO2
→ global warming

Question 12

Why are alkanes cracked?

Answer 12

To turn a long chain alkane, with is not very
economically valuable, into a shorter chain
alkane (more economically valuable as can be
used as a fuel) and an alkene (more reactive,
starting point for many products)

Question 13

What are the conditions for
thermal cracking?

Answer 13

700-1200 K temperature
Up to 7000 kPa pressure

Question 14

What is the intermediate for
the reaction?

Answer 14

Free radicals

Question 15

What are the main products
of thermal cracking?

Answer 15

alkenes

Question 16

What are the conditions for
catalytic cracking?

Answer 16

Lower temp (720K)
Lower pressure (but above atmospheric)
Zeolite catalyst (SiO2 and Al2O3) with a
honeycomb structure to give a large surface area

Question 17

What are the main products
of catalytic cracking?

Answer 17

Cycloalkanes, aromatic hydrocarbons,
branched alkanes

Question 18

Write an equation for the
combustion of propane

Answer 18

C3H8
+ 5O2 → 3CO2 + 4H2O

Question 19

What is a fuel?

Answer 19

Something which releases heat energy
when combusted

Question 20

What are the five main fuels
comprising of alkanes?

Answer 20

Methane, butane, propane, petrol (about
C8), paraffin (C10 - C18)

Question 21

What is incomplete
combustion and what
products are formed in the
case of alkanes?

Answer 21

Combustion in a limited supply of oxygen
CO - carbon monoxide - poisonous
C - carbon - particulates - soot - global dimming

Question 22

Which type of hydrocarbons
are most likely to undergo
incomplete combustion?

Answer 22

Longer chains

Question 23

What is the environmental
impact of carbon monoxide?

Answer 23

It is toxic/poisonous

Question 24

What is the environmental
impact of nitrogen oxides?

Answer 24

form nitric acid → acid rain,
photochemical smog

Question 25

What is the environmental
impact of sulfur
impurities/sulfur
dioxide

Answer 25

form sulphuric acid → acid rain

Question 26

What is the environmental
impact of soot (carbon)?

Answer 26

asthma, cancer, global dimming

Question 27

What is the environmental
impact of unburnt
hydrocarbons?

Answer 27

Photochemical smog

Question 28

What is the environmental
impact of carbon dioxide?

Answer 28

greenhouse gas → global warming,
increases global temperatures,
speeds up climate change

Question 29

What is the environmental
impact of water vapour?

Answer 29

greenhouse gas → global warming,
increases global temperatures,
speeds up climate change

Question 30

What are flue gases?

Answer 30

Gases given out by power stations

Question 31

Write two equations for two
different ways of
desulfurising flue gases.

Answer 31

CaO (s) + 2H2O (l) + SO2 (g) + ½O2 (g) → CaSO4.2H2O (s)
Or CaCO3 (s) + SO2 (g) + ½O2 (g) → CaSO4+ CO2 (g)

Question 32

What are catalytic
converters made up of?

Answer 32

Ceramic honeycomb coated with
platinum, palladium and rhodium (Pt,
Pd and Rh) metals

Question 33

What do catalytic converters
catalyse (equations)?

Answer 33

They catalyse these reactions of products from
car exhausts:
2CO (g) + 2NO (g) → N2 (g) + 2CO2 (g)
Hydrocarbons + NO → N2
+ CO2
+ H2O

Question 34

What are greenhouse
gases?

Answer 34

Gases which trap infrared radiation,
making the earth act like a greenhouse

Question 35

What is the greenhouse
effect and how does it
contribute to global
warming?

Answer 35

Greenhouse gases trap infrared radiation in the
atmosphere, atmosphere heats up → global
warming

Question 36

Define carbon neutral
activities

Answer 36

Activities that produce no net / overall
carbon dioxide emissions

Question 37

How are halogenoalkanes
formed from alkanes?

Answer 37

Free radical substitution reaction

Question 38

What are the three stages of
free radical substitution?

Answer 38

Initiation - breaking halogen bond to form free radicals
Propagation - chain part of the reaction where products are
formed but free radical remains
Termination - free radicals removed, stable products formed

Question 39

What are the conditions
needed for the formation of a
free radical chlorine atom?

Answer 39

Presence of UV light

Question 40

Write equations for the
reaction of CH with
form CH3Cl
Cl2 to

Answer 40

Initiation: Cl2 → 2Cl* (in presence of UV light)
Propagation: Cl* + CH4 → HCl + CH3
CH3 + Cl2 → CH3Cl + Cl
Termination:
CH3 + Cl → CH3Cl
2Cl → Cl2
*CH3+ *CH3→ CH3CH3

or
Cl2 → 2Cl*
: Cl* + CH4 → HCl + CH3
CH3 + Cl2 → CH3Cl + Cl
2Cl → Cl2

Question 41

What is the ozone layer’s
function?

Answer 41

protects the earth from harmful exposure to too many UV rays

Question 42

How do CFCs break the
ozone layer down?

Answer 42

Free radical substitution

Question 43

Write an equation for the
overall decomposition of
ozone into oxygen (O2)

Answer 43

2O3→ 3O2

Question 44

Write free radical
substitution equations to
show how Cl free radicals
catalyse the break down of
O3

Answer 44

Cl2 → 2Cl* (in presence of UV light)
Cl* + O3→ ClO* + O2
ClO* + O3 → 2O2 + Cl*
Overall: 2O3→ 3O2