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Organic Chemistry > 3.3.2 Alkanes > Flashcards

3.3.2 Alkanes Flashcards

1
Q

what is the general formula of an alkane?

A

CnH2n+2

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2
Q

what is the general formula of cycloalkanes?

A

CnH2n

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3
Q

What is an alkane?

A

saturated hydrocarbon containing C-H bonds only

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3
Q

Are alkanes’ bonds 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

No, hydrogen bonds in water are stronger than alkanes’ Van der Waals forces

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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
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
Non renewable

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9
Q

What is fractional distillation? How does it work?

A

Crude oil heated until it is vaporised
Passed into a fractioning tower that is cooler at the top than the bottom
Vapours rise up the column and - via trays and bubble caps - condense when temperature is lower than their boiling point
Shorter chain alkanes condense at the top - they have the lowest boiling points

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10
Q

Why are alkanes cracked?

A

to turn a long chain alkane into shorter ones and an alkene.
Shorter chains are more useful

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11
Q

What are the conditions for Thermal cracking?

A

700-1200K temp
Up to 7000kPa pressure

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12
Q

What is the intermediate for the thermal cracking reaction?

A

Free radicals

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13
Q

What are the main products of thermal cracking?

A

Alkenes

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14
Q

What are the conditions for catalytic cracking?

A

Lower temperature
Lower pressure
Zeolite catalyst with a honeycomb structured give a large SA

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15
Q

What are the main products of catalytic cracking?

A

Cycloalkanes, aromatic hydrocarbons, branched alkanes

16
Q

Write an equation for the combustion of propane.

A

C3H8 + 5O2 —> 3CO2 + 4H2O

17
Q

What is a fuel?

A

Something which releases heat energy when combusted

18
Q

What are the five main fuels comprising of alkanes?

A

Methane, butane, propane, petrol, paraffin

19
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

20
Q

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

A

Longer chains

21
Q

What is the environmental impact of carbon monoxide?

A

Toxic / poisonous

22
Q

What is the environmental impact of nitrogen oxides?

A

Form nitric acid —> acid rain, smog

23
Q

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

A

Form sulphuric acid —> acid rain

24
Q

What is the environmental impact of soot (carbon)?

A

Asthma, cancer, global dimming

25
Q

What is the environmental impact of unburnt hydrocarbons?

A

Smog

26
Q

What is the environmental impact of carbon dioxide?

A

Greenhouse gas —> global warming

27
Q

What is the environmental impact of water vapour?

A

Greenhouse gas —> global warming

28
Q

What are flue gases?

A

Gases given out by power stations

29
Q

What can we use to desulphurise flue gases?

A

CaO
CaCO3

30
Q

What are catalytic converters made up of?

A

Ceramic honeycomb coated with platinum, palladium and rhodium metals

31
Q

What are greenhouse gases?

A

Gases which trap infrared radiation, making earth like a greenhouse

32
Q

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

A

Greenhouse gases trap infrared radiation in the atmosphere, atmosphere heats up

33
Q

Define carbon neutral activities?

A

Produce no net / overall carbon dioxide emissions

34
Q

How are halogenoalkanes formed from alkanes?

A

Free radical substitution reactions

35
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

36
Q

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

A

Presence of UV light

37
Q

What is the ozone layer’s function?

A

Protects the earth from harmful exposure to too many UV rays

38
Q

How do CFCs break the ozone layer down?

A

Free radical substitution

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