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Chemistry > Alkanes > Flashcards

Alkanes Flashcards

1
Q

What is an alkane?

A

A saturated hydrocarbon containing C-H bonds only

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2
Q

What is the general formula of an alkane?

A

CnH2n+2

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3
Q

Are the bonds in alkanes polar? Why/why not?

A

Non-polar - carbon and hydrogen have similar electronegativities

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4
Q

Which intermolecular forces do alkanes have? Why?

A

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

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5
Q

Are alkanes soluble in water? Why?

A

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

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6
Q

How reactive are alkanes?

A

Very unreactive

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7
Q

Which reactions will alkanes undergo?

A

Combustion and reaction with halogens

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8
Q

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

A

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

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9
Q

Name the fractions from

high to low boiling point.

A 
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
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10
Q

What is fractional distillation/how does it work?

A

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

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11
Q

What is fracking and how is it done?

A

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

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12
Q

Pros/cons of fracking?

A

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

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13
Q

Why are alkanes cracked?

A

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)

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14
Q

What are the conditions for thermal cracking?

A

700-1200K (1000 degrees C)

70 atm

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15
Q

What is the intermediate for the reaction?

A

Free radicals

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16
Q

What are the main products of thermal cracking?

A

Alkenes

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17
Q

What are the conditions for catalytic cracking?

A 
Lower temp (720K)
Lower pressure (but above atmospheric)
Zeolite catalyst (SiO2, and Al203) with a
honeycomb structure to give a large surface area
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18
Q

What are the main products of catalytic cracking?

A

Cycloalkanes, aromatic hydrocarbons, branched alkanes

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19
Q

Write an equation for the combustion of propane

A

C3H8 + 5O2 –> 3CO2 + 4H2O

20
Q

What is a fuel?

A

Something which releases heat energy when combusted

21
Q

what are the five main fuels comprising of alkanes?

A

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

22
Q

What is incomplete combustion and what products

are formed in the case of alkanes?

A

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

23
Q

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

A

Longer chains

24
Q

What is the environmental impact of carbon monoxide?

A

It is toxic/poisonous

25
Q

What is the environmental impact of nitrogen oxides?

A

Form nitric acid –> acid rain, photochemical smog

26
Q

What is the environmental impact of sulfur impurities/ sulfur dioxide?

A

Form sulfuric acid –> acid rain

27
Q

What is the environmental impact of soot (carbon)?

A

asthma, cancer, global dimming

28
Q

What is the environmental impact of unburnt hydrocarbons?

A

Photochemical smog

29
Q

What is the environmental impact of carbon dioxide?

A

greenhouse gas –> global warming, increases global temperatures, speeds up climate change

30
Q

What is the environmental impact of water vapour?

A

greenhouse gas –> global warming, increases global temperatures, speeds up climate change

31
Q

What are flue gases?

A

Gases given out by power stations

32
Q

Write two equations for two different ways of desulfurising flue gases

A 
CaO(s) + 2H2O(l) + SO2(g) + 1/2O2(g) --> CaSO4.2H2O(s)
Or CaCO3(s) + SO2(g) + 1/2O2(g) --> CaSO4 + CO2(g)
33
Q

What are catalytic converters made up of?

A

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

34
Q

What do catalytic converters catalyse (equations)?

A

They catalyse these reactions of products from
car exhausts:
2CO (g) + 2NO (g) -› N2 (g) + 2CO2 (g)
Hydrocarbons + NO –> N2 + CO2 + H20

35
Q

What are greenhouse gases?

A

Gases which trap infrared radiation,

making the earth act like a greenhouse

36
Q

What is the greenhouse effect and how does it

contribute to global warming?

A

Greenhouse gases trap infrared radiation in the

atmosphere, atmosphere heats up –› global warming

37
Q

Define carbon neutral activities

A

Activities that produce no net/overall carbon dioxide emissions

38
Q

How are halogenoalkanes formed from alkanes?

A

Free radical substitution

39
Q

What are the three stages of free radical

substitution?

A

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

40
Q

What are the conditions needed for the formation of

a free radical chlorine atom?

A

Presence of UV light

41
Q

Write equations for the reaction of CH4 with Cl2 to

form CH3CI

A 
Initiation: Cl2 -› 2CI• (in presence of UV light)
Propagation: Cl• + CH4 --> HCI + •CH3
•CH3 + Cl2 - CH3CI + CI•
Termination:
•CH3 + Cl• --> CH3Cl
2Cl• --> CI2
•CH3 + •CH3 --> CH3CH3
42
Q

What is the ozone layer’s function?

A

Protects the earth from harmful exposure to too many UV rays

43
Q

How do CFCs break down the ozone layer?

A

Free radical substitution

44
Q

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

A

2O3 –> 3O2

45
Q

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

A

Cl2 -› 2Cl• (in presence of UV light)
CI• + O3 –> CIO• + O2
CIO• + O3 –> 2O2 + CI•
Overall: 2O3 –> 3O2

Chemistry (3 decks)

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