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

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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

25
How is ozone produced in combustion of hydrocarbons?
Hydrocarbons react with NOₓ to form O₃
26
Effect of CO
Toxic gas (binds with heamoglobin)
27
Effect of C released in incomplete combustion
Exacerbate asthma
28
Effect of NOₓ
- Acid rain (dissolves in water to form nitric acid) - Photochemical smog
29
How is NOₓ produced in combustion of hydrocarbons?
Nitrogen and oxygen from the air react at high temperatures (in engines) to form NOₓ
30
Effect of sulfur dioxide
Acid rain (dissolved in water to form sulfuric acid)
31
How is sulfur dioxide produced in combustion of hydrocarbons?
Sulfur from fuel impurities reacts with oxygen from the air
32
What do catalytic converters remove from exhaust gas?
CO, NO, and unburned hydrocarbons
33
Two features of catalytic converters
- Honeycombed structure - Thin layer of metal catalyst
34
Metals used in catalytic converters
Pt (platinum) Pd (palladium) Rh (rhodium)
35
Why is a thin layer of catalyst used in catalytic converters?
Reduces amount of catalyst used (reduces cost)
36
Why is a honeycomb structure used in catalytic converters?
Provides a large surface area (faster rate of reaction)
37
How are NO and CO removed in catalytic converters?
Reacted together to form less polluting products
38
How are unburned hydrocarbons removed in catalytic converters?
Reaction with O₂ or NO
39
What are flues coated with to absorb and react with sulfur dioxide?
Calcium oxide or calcium carbonate
40
Products when calcium oxide or calcium carbonate react with sulfur dioxide
Calcium sulfate (IV) CaSO₄ (+CO₂ with calcium carbonate)
41
How is solid Calcium sulfate (IV) produced from flue gas disposed of?
Buried in disused mines or oil wells
42
Heterogeneous catalyst
A catalyst that is in a different state to the reactants
43
What is the energy from UV light used for when forming halide radicals?
Breaking the bond within the molecules