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Alevel Chemistry PMT and key words > (PMT) Alkanes > Flashcards

(PMT) Alkanes Flashcards

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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 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

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

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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12
Q

What are the conditions for

thermal cracking?

A

700-1200 K temperature (about 1000C)

Up to 70 atm pressure (up to 7000 kPa)

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13
Q

What is the intermediate for

the reaction?

A

Free radicals

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14
Q

What are the main products

of thermal cracking?

A

alkenes

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15
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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16
Q

What are the main products

of catalytic cracking?

A

Cycloalkanes, aromatic hydrocarbons,

branched alkanes

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17
Q

Write an equation for the (complete) combustion of propane

A

C3H8 + 5O2 → 3CO2+ 4H2O

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18
Q

What is a fuel?

A

Something which releases heat energy

when combusted

19
Q

What are the five main fuels

comprising of alkanes?

A

Methane, butane, propane, petrol (about

C8), paraffin (C10 - C18)

20
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

21
Q

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

A

Longer chains

22
Q

What is the environmental

impact of carbon monoxide?

A

It is toxic/poisonous

23
Q

What is the environmental

impact of nitrogen oxides?

A

form nitric acid → acid rain,

photochemical smog

24
Q

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

A

form sulphuric acid → acid rain

25
Q

What is the environmental

impact of soot (carbon)?

A

asthma, cancer, global dimming

26
Q

What is the environmental
impact of unburnt
hydrocarbons?

A

Photochemical smog

27
Q

What is the environmental

impact of carbon dioxide?

A

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

28
Q

What is the environmental

impact of water vapour?

A

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

29
Q

What are flue gases?

A

Gases given out by power stations

30
Q

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

A
  1. CaO (s) + 2H2O (l) + SO2(g) + ½O2(g) → CaSO4.2H2O (s)

2. CaCO3(s) + SO2(g) + ½O2(g) → CaSO4+ CO2(g)

31
Q

What are catalytic

converters made up of?

A

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

32
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

33
Q

What are greenhouse

gases?

A

Gases which trap infrared radiation,

making the earth act like a greenhouse

34
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

35
Q

Define carbon neutral

activities

A

Activities that produce no net / overall

carbon dioxide emissions

36
Q

How are halogenoalkanes

formed from alkanes?

A

Free radical substitution reaction

37
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

38
Q

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

A

Presence of UV light

39
Q

Write equations for the
reaction of CH4 with Cl2 to
form CH3Cl

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

40
Q

What is the ozone layer’s

function?

A

protects the earth from harmful exposure to too many UV rays

41
Q

How do CFCs break the

ozone layer down?

A

Free radical substitution

42
Q

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

A

2O3→ 3O2

43
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

Alevel Chemistry PMT and key words (5 decks)

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