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Chemistry > Alkanes > Flashcards

Alkanes Flashcards

1
Q

What is an alkane?

A

A saturated hydrocarbons
containing C-H bonds only

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2
Q

What is the general formula
of an alkane?

A

Cn H2n+2

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3
Q

Are their bonds polar?
Why/why not?

A

Nonpolar- carbon and
hydrogen have similar
electronegativities

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4
Q

Which intermolecular forces
do they have? Why?

A

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

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5
Q

Are they soluble in water?
why?

A

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

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6
Q

Which reactions will alkanes
undergo?

A

Combustion and reaction with
halogens

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7
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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7
Q

How reactive are alkanes?

A

Very unreactive

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8
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
https://bit.ly/pmt-ed

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9
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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10
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
HCl and methanol added to break up shale and prevent
corrosion

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11
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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12
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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13
Q

What are the conditions for
thermal cracking?

A

700-1200 K temperature
Up to 7000 kPa pressure

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14
Q

What is the intermediate for
the reaction?

A

Free radicals

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15
Q

What are the main products
of thermal cracking?

A

alkenes

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16
Q

What are the conditions for
catalytic cracking?

A

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

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17
Q

What are the main products
of catalytic cracking?

A

Cycloalkanes, aromatic hydrocarbons,
branched alkanes

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18
Q

Write an equation for the
combustion of propane

A

C3H8
+ 5O2 → 3CO2 + 4H2O

19
Q

What is a fuel?

A

Something which releases heat energy
when combusted

20
Q

What are the five main fuels
comprising of alkanes?

A

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

21
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

22
Q

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

A

Longer chains

23
Q

What is the environmental
impact of carbon monoxide?

A

It is toxic/poisonous

24
Q

What is the environmental
impact of nitrogen oxides?

A

form nitric acid → acid rain,
photochemical smog

25
Q

What is the environmental
impact of sulfur
impurities/sulfur
dioxide

A

form sulphuric acid → acid rain

26
Q

What is the environmental
impact of soot (carbon)?

A

asthma, cancer, global dimming

27
Q

What is the environmental
impact of unburnt
hydrocarbons?

A

Photochemical smog

28
Q

What is the environmental
impact of carbon dioxide?

A

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

29
Q

What is the environmental
impact of water vapour?

A

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

30
Q

What are flue gases?

A

Gases given out by power stations

31
Q

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

A

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

32
Q

What are catalytic
converters made up of?

A

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

33
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
+ H2O

34
Q

What are greenhouse
gases?

A

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

35
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

36
Q

Define carbon neutral
activities

A

Activities that produce no net / overall
carbon dioxide emissions

37
Q

How are halogenoalkanes
formed from alkanes?

A

Free radical substitution reaction

38
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

39
Q

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

A

Presence of UV light

40
Q

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

A

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

41
Q

What is the ozone layer’s
function?

A

protects the earth from harmful exposure to too many UV rays

42
Q

How do CFCs break the
ozone layer down?

A

Free radical substitution

43
Q

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

A

2O3→ 3O2

44
Q

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

A

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

Chemistry (16 decks)

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