Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

AQA A Level Chemistry > 12 - Alkanes > Flashcards

12 - Alkanes Flashcards

1
Q

Are alkanes saturated or unsaturated?

A

Saturated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Physical Properties of alkanes

A
  • polarity
  • boiling points
  • solubility
  • reactivity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Polarity

A

Alkanes are almost non polar because the electronegativities of carbon and hydrogen are similar

The intermolecular forces between their molecules are weak van dear Waals forces

The larger the molecule, the larger the vdW force

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Solubility of alkanes

A

Insoluble in water

Water molecules are held together by hydrogen bonds which are much stronger than the vdW forces that act between alkane molecules,

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Boiling points of alkanes

A

As the length of the alkane chain increases, so does the boiling point. This is because the intermolecular forces increase meaning more energy is required to break the bonds.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Reactivity of alkanes

A

Alkanes are relatively unreal it. They have strong carbon-carbon and carbon-hydrogen bonds

They don’t react with: acids, bases, oxidising agents or reducing agents.

However, they burn and react with halogens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Products of complete combustion

A

Carbon dioxide + Water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Products of incomplete combustion

A

Carbon/Carbon monoxide + water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When to know if carbon monoxide or carbon is produces

A

Carbon monoxide: a poisonous gas is produces
Carbon: black product (soot)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are alkanes used as

A

Fuels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Why are alkanes good fuels

A

Combustion reactions give out heat and have negative enthalpy changes. Which means lots of heat is given out basically so it is a good fuel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Different pollutants produced as a results of burning alkanes

A

Carbon monoxide
Nitrogen oxides
Sulfur dioxide
Carbon particulates
Unburnt hydrocarbons
Carbon dioxide
Water vapour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why is carbon monoxide a pollutant

A

Poisonous gas

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Why are nitrogen oxides a pollutant

A

Oxides react with water vapour and oxygen in the air to form nitric acid —> acid rain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How are nitrogen oxides produced?

A

Under extreme heat and pressure

N2 + O2 -> 2NO

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How is Sulfur dioxide produced?

A

Produced from Sulfur containing impurities present in crude oil

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Negativity of Sulfur dioxide

A

Combines with water vapour and oxygen in the air to form Sulfuric acid —> acid rain

18
Q

Negatives of carbon particles

A

Very small, easy to enter the body

19
Q

Negatives of unburnt hydrocarbons

A

Easy for them to enter the atmosphere and they are significant greenhouse gases.
They contribute to photochemical smog which can cause a variety of health problems

20
Q

Negatives of CO2

A

Greenhouse gas -> climate change etc

21
Q

Negative of water vapour

A

Greenhouse gas

22
Q

Sulfur dioxide gas ‘nickname’

A

Flue gases

23
Q

Equation for how sulfuric acid is produced

A

SO2 + 0.5O2 + H2O —> H2SO4

24
Q

How can calcium oxide remove flue gas?

A

Calcium oxide (lime) and water are sprayed into the flue gas which forms calcium sulphite
This is further oxidised to calcium sulphate aka gypsum

25
Q

Equation for calcium sulphide flue gas desulfurisation

A

CaO + 2H20 + SO2 + 0.5O2 -> CaSO4.2H20

26
Q

Equation for the calcium carbonate (limestone) flue gas desulfurisation

A

CaCo3 + 0.5O2 + SO2 —> CaSO4 + CO2

27
Q

What is a catalytic converter?

A

A honeycomb,b made of a ceramic material coated with ceramic and rhodium metals
They reduce the output of carbon monoxide, nitrogen oxides and unburnt hydrocarbons in the exhaust gas mixture

28
Q

Equation for how a catalytic converter removes carbon monoxide and nitrogen oxide

A

2CO + NO —> N2 +2CO2

29
Q

Equation for how a catalytic converter removes hydrocarbons and nitrogen oxide

A

Hydrocarbons + Nitrogen oxide —> Nitrogen + Carbon Dioxide + Water

Eg C9H18 + 25NO —> 12.5N2 + 8CO2 + 9H20

30
Q

What is a free radical?

A

A free radical is any species with an unpaired electron

31
Q

What is needed for free radical substitution to occur

A

UV light

32
Q

Initiation step with free radical substitution

A

First, you need to break the covalent bond between the halogens

Eg: Cl—Cl—> 2Cl•

33
Q

Why does the Cl bond break?

A

The chlorine molecule absorbs the energy of a single quantum of UV light. The energy of one quantum of UV light is greater than the Cl—Cl bond energy, so the bond will break.

34
Q

Propagation step 1, what happens?

A

The chlorine free radical takes a hydrogen atom from the alkane to form hydrogen (halogen)

CH4 + Cl• —> CH3• + HCl

35
Q

Propagation step 2, what happens?

A

The methyl free radical is now very reactive and reacts with a chlorine e molecule. This produces another chlorine free radical and a molecule of chloromethane

•CH3 + Cl2 —> CH3Cl + Cl•

36
Q

What is the effect of propagation?

A

To produce hydrogen chloride, chloromethane and a new Cl• free radical. This is ready to react with more methane and repeat the 2 steps.

37
Q

What happens in termination

A

The free radicals are removed
This can happen in 3 ways:

Cl. + Cl. —> Cl2

.CH3 + .CH3 —> C2H6

Cl. + .CH3 —> CH3Cl

38
Q

What substances are destroying the ozone layer?

A

Chlorofluorocarbons (CFCs)

39
Q

Why is the ozone layer important?

A

It protects the Earth from the harmful exposure to too many UV rays.

40
Q

How are chlorine free radicals formed?

A

Chlorine free radicals are formed from CFCs because the C—Cl bond breaks homolytically in the presence of UV radiation to produce chlorine free radicals, Cl. These then attack the ozone molecules

41
Q

Equation for how Cl free radicals attack the ozone:

A

Cl. + O3 —> ClO. + O2

ClO. + O2 —> 2O2 + Cl.

The chlorine free radical isn’t destroyed, it acts as a catalyst in the breakdown of ozone to oxygen

2O3 —> 3O2

AQA A Level Chemistry (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions