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AQA A-Level Chemistry > 3.2 Alkanes > Flashcards

3.2 Alkanes Flashcards

1
Q

General formula of alkanes

A

CₙH₂ₙ₊₂

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2
Q

Shape around C atoms in alkanes

A

Tetrahedral (all have 4 bond pairs)

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3
Q

General formula of cyclic alkanes

A

CₙH₂ₙ

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4
Q

Are alkanes polar?

A

No, they contain no polar bonds

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5
Q

Structure + bonding of alkanes

A
  • Simple molecular
  • van der Waals’ forces between molecules
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6
Q

Are alkanes soluble in water?

A

No. Hydrogen bonds between water molecules are much stronger than the van der Waals’ forces in alkanes

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7
Q

Effect of increasing chain length on boiling point of alkanes

A

As chain length increases b.p increases.

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8
Q

Why does b.p of alkanes increase with chain length?

A
  • More electrons in molecules
  • So stronger van der Waals’ forces
  • More energy needed to overcome these
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9
Q

Effect of increasing number of branches on boiling point of alkanes

A

As number of branches increases, b.p decreses

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10
Q

Why does b.p of alkanes decrease with increasing number of branches?

A
  • Fewer points of contact between molecules
  • Weaker van der Waals’ forces
  • Less energy needed to overcome these
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11
Q

Two types of cracking

A

Catalytic and thermal

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12
Q

Conditions for thermal cracking

A
  • very high temperature
  • very high pressure
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13
Q

Products of thermal cracking

A

Alkanes and a high percentage of alkenes

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14
Q

Uses of the products of thermal cracking

A

Making polymers

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15
Q

Conditions for catalytic cracking

A
  • High temperature
  • Slight pressure
  • Zeolite catalyst
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16
Q

Products of catalytic cracking

A

Cycloalkanes, branched alkanes, and aromatic hydrocarbons

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17
Q

Uses of the products of catalytic cracking

A

Motor fuels

18
Q

Products of complete combustion of hydrocarbons

A

Carbon dioxide and water

19
Q

Products of incomplete combustion of hydrocarbons

A

Carbon monoxide and water

20
Q

When does incomplete combustion occur?

A

In a limited supply of oxygen

21
Q

Products of further incomplete combustion

A

Solid carbon and water

22
Q

When does further incomplete combustion occur?

A

In a very limited supply of oxygen

23
Q

Effect of unburned hydrocarbons

A

Forms ozone in the lower atmosphere, which can cause respiratory problems

24
Q

Ozone

A

O₃

25
Q

How is ozone produced in combustion of hydrocarbons?

A

Hydrocarbons react with NOₓ to form O₃

26
Q

Effect of CO

A

Toxic gas (binds with heamoglobin)

27
Q

Effect of C

A

Exacerbate asthma

28
Q

Effect of NOₓ

A
  • Acid rain (dissolves in water to form nitric acid)
  • Photochemical smog
29
Q

How is NOₓ produced in combustion of hydrocarbons?

A

Nitrogen and oxygen from the air react at high temperatures (in engines) to form NOₓ

30
Q

Effect of sulfur dioxide

A

Acid rain (dissolved in water to form sulfuric acid)

31
Q

How is sulfur dioxide produced in combustion of hydrocarbons?

A

Sulfur from fuel impurities reacts with oxygen from the air

32
Q

What do catalytic converters remove from exhaust gas?

A

CO, NO, and unburned hydrocarbons

33
Q

Two features of catalytic converters

A
  • Honeycombed structure
  • Thin layer of metal catalyst
34
Q

Metals used in catalytic converters

A

Pt (platinum)
Pd (palladium)
Rh (rhodium)

35
Q

Why is a thin layer of catalyst used in catalytic converters?

A

Reduces amount of catalyst used (reduces cost)

36
Q

Why is a honeycomb structure used in catalytic converters?

A

Provides a large surface area (faster rate of reaction)

37
Q

How are NO and CO removed in catalytic converters?

A

Reacted together to form less polluting products

38
Q

How are unburned hydrocarbons removed in catalytic converters?

A

Reaction with O₂ or NO

39
Q

What are flues coated with to absorb and react with sulfur dioxide?

A

Calcium oxide or calcium carbonate

40
Q

Products when calcium oxide or calcium carbonate react with sulfur dioxide

A

Calcium sulfate (IV) CaSO₄ (+CO₂ with calcium carbonate)

41
Q

How is solid Calcium sulfate (IV) produced from flue gas disposed of?

A

Buried in disused mines or oil wells

AQA A-Level Chemistry (9 decks)

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