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✅Chemistry Unit 2 > đŸ”´đŸ”¸2.5 -hydrocarbons > Flashcards

đŸ”´đŸ”¸2.5 -hydrocarbons Flashcards

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1
Q

What is a fossil fuel

A

A fuel that is derived from organisms that lived long ago

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2
Q

What is a non-renewable resource

A

A resource that can’t be reformed in a reasonable timescale

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3
Q

What is a greenhouse gas

A

A gas that causes an increase in the earths temperature

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4
Q

Name some examples of fossil fuels

A

Natural gas, petroleum and coal

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5
Q

Name some advantages of using fossil fuels

A

1) available in a variety of forms allowing the type of fuel to be matched to its use e.g coal in power stations
2) can be split into fractions for varied uses e.g petroleum
3) available at all time, some green sources e.g solar and wind have limited availability

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6
Q

Name the disadvantages of fossil fuels

A

1) non renewable, formation of fossil fuels takes millions of years and reserves are being used faster than those formed
2) combustion of fossil fuels produces carbon dioxide which causes global warming and climate change
3) acid rain formation
4) formation of carbon monoxide

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7
Q

How does carbon dioxide cause climate change

A

Carbon dioxide absorbs infrared radiation from the earths surface and emits it in all directions, some goes back to the earths surface causing an increase in surface temperature

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8
Q

Name 2 problems caused by global warming

A

Rising sea levels
Changes to crop suitability
Acid rain
Carbon monoxide formation

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9
Q

How is nitric acid in acid rain formed

A

N2 (g) + O2 (g) —> 2NO (g)

2NO (g) + O2 (g) —> 2NO2 (g)

2NO2 (g) + H2O (l) —> HNO3 (g) + HNO2 (aq)

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10
Q

Name 3 greenhouse gases present In the atmosphere

A

Water
Carbon dioxide
Methane

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11
Q

How is sulfuric acid formed which is present in acid rain

A

H2O (l) + SO2 (g) —> H2SO3 (aq)

H2SO3 (aq) + 1/2O2 (g) —> H2SO4 (aq)

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12
Q

What damage do sulfuric acid and nitric acid in acid rain cause?

A

Damage to buildings especially those containing calcium carbonate
Lower pH of lakes/rivers harming aquatic life e.g fish
Damage trees/forests

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13
Q

Describe how fossil fuels lead to an increase in carbon monoxide

A

When fossil fuels aren’t burnt in excess oxygen incomplete combustion occurs forming Carbon monoxide.
CO is toxic as it binds with haemoglobinin blood so that it is not available to carry oxygen around the body

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14
Q

Non health related problem of carbon monoxide

A

Incomplete combustion is less efficient than combustion e.g a car would achieve fewer miles per litre of fuel

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15
Q

What is the general formula for the homologous series of alkanes

A

CnH(2n+2)

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16
Q

What is the difference between each consecutive member of the homologous series of alkanes

A

CH2

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17
Q

Do all alkanes have similar chemical reactions?

A

Yes as they are all saturated hydrocarbons

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18
Q

What states do small, larger and large alkanes have at room temperature?

A

Small alkanes are gases at room temp (methane), larger ones are liquids (petrol) and larger ones are solids (wax candles)

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19
Q

Why are alkanes non polar?

A

Non polar since the electronegatives of carbon and hydrogen are similar

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20
Q

Are alkanes reactive? What exceptions

A

Generally unreactive as they have no double bonds

-two important reactions = combustion and Halogenation

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21
Q

Define complete combustion

A

Combustion that occurs in excess oxygen

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22
Q

Define incomplete combustion

A

Combustion that occurs in insufficient oxygen

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23
Q

Is combustion exothermic or endothermic?

A

Exothermic as it involves a release of energy into its surroundings

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24
Q

What are the products of complete combustion

A

Carbon dioxide and water

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25
Q

What are the products of incomplete combustion

A

Carbon monoxide and water

Can sometimes form carbon as seen in black smoke from an engine

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26
Q

What is halogenation?

A

A reaction with any halogen

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27
Q

What is initiation

A

The reaction that starts the process of halogenation

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28
Q

What is homolytic bond fission

A

When a bond is broken and each of the bonded atoms receives one of the bonded electrons

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29
Q

What is a radical

A

A species with an unpaired electron

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30
Q

What is propagation

A

The reaction by which a radical is used as a reactant and forms a radical as a product continuing the reaction

31
Q

What is a chain reaction

A

A reaction which involves a series of steps and once started continues

32
Q

What is termination

A

The reaction that ends a process

33
Q

What is a reaction mechanism

A

The stages by which a reaction proceeds e.g reaction mechanism for halogenation is initiation, propagation, and termination

34
Q

What is a substitution reactions

A

One where one atom/group is replaced by another atom/group

35
Q

What are the conditions for halogenation to occur

A

Alkanes don’t react with halogens in the dark :: they must be exposed to UV light (often sunlight) to react

36
Q

What are the 3 stages of halogenation

A

1) initiation
2) propagation
3) termination

37
Q

Describe initiation in detail

A

1) UV light has sufficient energy to break Cl-Cl bond (any halogen) homolytically.
2) homolytic bond fission occurs when each of the bonded atoms receives one fo the bond electrons so radicals are formed
3) radicals react indiscriminately to gain another electron and form a pair

38
Q

Equations for initiation

A

Cl2 —> 2Cl •

Note: • = radical

39
Q

Describe propagation in detail

A

1) Radicals are very reactive and take part in a series of propagation reactions
2) chain reaction occurs.

40
Q

Equations for propagation

A

Cl• + CH4 —> CH3• + HCL

CH3• + Cl2 —> CH3Cl + Cl•

41
Q

Describe termination in detail

A

Propagation continues until 2 radicals meet causing reaction to stop.

42
Q

Equation for termination

A

Cl• + CH3• —> CH3Cl

43
Q

Why are alkanes unreactive and why are radicals reactive

A

Alkanes are unreactive because they are non polar and do not contain double bonds whereas radicals are very reactive because they have an unpaired electron

44
Q

What is a π bond

A

A bond formed by the sideways overlap of p electrons

45
Q

What is the general formula of alkenes

A

CnH(2n)

46
Q

When are alkenes formed?

A

When petroleum is cracked

47
Q

Why are alkenes much more reactive than alkanes?

A

Due to their double bond

48
Q

What is a main use of alkenes

A

Important starting material for a variety of organic synthesis reactions e.g polymerisation

49
Q

According to VSEPR theory which shape/bond angle is Ethene

A

Planar triangular with a bond angle of 120 degrees

50
Q

What does a pi bond have

A

A pi bond has an area of High electron density above and below the plane of the molecule

51
Q

Why are alkenes not used as fuels

A

They have to be manufactured from alkanes :: it is more cost effective to use alkanes directly themselves

52
Q

Name the general bond angles in other alkenes

A

120 degrees between hydrogen bonds attached to the double bonded carbon atom
109.5 degrees between hydrogen bonds attached to normal sigma carbon atoms

53
Q

What is an electrophile

A

An electron deficient species that can accept a lone pair of electrons

54
Q

What is heterolytic bond fission

A

When a bond is broken and one of the bonded atoms receives both the bonded electrons

55
Q

What is an addition reaction

A

A reaction in which reagents combine to give one product

56
Q

How many electrons do alkenes have in pi orbital

What does this mean

A

Pair of electrons
This means they are susceptible to attack by an electrophile

(LEARN DIAGRAMS IN BOOK)

57
Q

What is added to a substance to identify an alkene

What happens as a positive result

A

Bromine/bromine water as it tests for unsaturated hydrocarbons
Decolouration of Brown bromine water

58
Q

Why is bromine water used instead of liquid bromine

A

Because liquid bromine is very corrosive

59
Q

What process occurs if you add hydrogen to an alkene

A

Hydrogenation

60
Q

What catalyst is used during hydrogenation

A

Transition metals such as platinum but nickel is most commonly used as its cheap

61
Q

Name a use of hydrogenation

A

Liquid vegetable oils are polyunsaturated (many double bonds) can be made saturated by adding hydrogen hardening oil to make solid edible fats (butter)

62
Q

What are the two possible products of the reaction between propane and hydrogen bromide

A

1-bromopropane
2-bromopropane

2-bromopropane is produced more frequently

63
Q

Why is 2 bromopropane the more dominant product of the reaction between propene and hydrogen bromide

A

Because the carbocation is more stable because alkyl groups tend to release electrons to become (^+) spreading (delocalising) the positive change and stabilising the ion. This means 2 carbocations as featured in forming 2-bromopropane are more stable than 1.

64
Q

What is polymerisation

A

The joining of a large number of monomer molecules to make a large polymer molecule

65
Q

What is a monomer

A

A small molecule that can be made into a polymer

66
Q

What undergoes addition polymerisation?

What is it?

A
  • Alkenes and substituted alkenes

- This means that the double bond is used to join the monomers and only 1 product forms

67
Q

What is formed when Ethene undergoes addition polymerisation

A

Polyethene commonly called polythene

Now does not contain double bond but involves ene

68
Q

Name some properties of polythene

A

Unreactive, flexible, solid used to make plastic bags

69
Q

What was influential in producing hard plastic

A

Catalysts such as Ziegler catalysts meant that chains could align closer, strengthening van der Waals forces and producing harder higher density plastic
Now had a higher melting point

70
Q

What is a repeat unit

A

The section of the polymer that is repeated to make the whole structure

71
Q

What is the use of polypropene

A

Rigid plastic used in food containers and general kitchen equipment
(LEARN DIAGRAM Pg 143)

72
Q

What is a use of polychloroethene

PVC

A

Used In water pipes, waterproof clothing etc

LEARN DIAGRAM Pg 144

73
Q

What is a use of polyphenylethene

Polystyrene

A

Insulator in packaging

✅Chemistry Unit 2 (8 decks)

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