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Chemistry > 3.2 Alkanes > Flashcards

3.2 Alkanes Flashcards

1
Q

Give the definition of a petroleum fraction.

A

A petroleum fraction is a mixture of hydrocarbons with a similar chain length and boiling point range.

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2
Q

Describe industrial fractional distillation in steps.

A

(see page 1 in the chemrevise revision guide)

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3
Q

What is the vacuum distillation unit in fractional distillation? What is the benefit of this?

A

(see page 1 in the chemrevise revision guide)

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4
Q

Describe how you would execute fractional distillation in the laboratory.

A

(see page 1 in the chemrevise revision guide)

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5
Q

Give the definition of cracking.

A

Cracking is the conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds

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6
Q

Give a general formula of cracking.

A

High Mr alkanes -> smaller Mr alkanes + alkenes + (hydrogen)

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7
Q

Cracking is a ______ process involving the splitting of strong _______ bonds so requires _____ temperatures.

A

Cracking is a chemical process involving the splitting of strong covalent bonds so requires high temperatures.

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8
Q

Fractional distillation is a ______ process involving the splitting of weak ________ forces between molecules.

A

Fractional distillation is a physical process involving the splitting of weak van der waals forces between molecules.

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9
Q

Draw a labelled diagram of fraction distillation in industry including the different fractions with the boiling points of each.

(8 fractions)

A

(see page 1 in the chemrevise revision guide)

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10
Q

What are the conditions of thermal cracking?

A
  • High pressure (7000kPa)

- High temperature (400ºC to 900ºC)

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11
Q

What are the conditions of catalytic cracking?

A
  • Slight or moderate pressure
  • High temperature (450ºC)
  • Zeolite catalyst
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12
Q

What products are produced from thermal cracking?

A
  • Mostly alkenes
    (e. g. ethene used for making polymers and ethanol)
  • Sometimes produces hydrogen
    (used in the Haber process and in the margarine manufacture)
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13
Q

What products are produced from catalytic cracking?

A
  • Branched and cyclic alkanes
    (burn more cleanly and are used to give fuels a higher octane number)
  • Aromatic hydrocarbons

(used for making motor fuels)

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14
Q

Is thermal or catalytic cracking cheaper? Explain why.

A

Catalytic cracking is cheaper than thermal cracking because it saves energy as lower temperatures and pressures are used.

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15
Q

Why are alkanes good as fuels?

A

Alkanes readily burn in the presence of oxygen. This combustion of alkanes is highly exothermic, explaining their use as fuels.

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16
Q

Give two example equations of thermal cracking.

A

(see page 2 in the chemrevise revision guide)

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17
Q

What is the definition of fuel?

A

Fuel releases heat energy when burnt.

18
Q

What are the products of complete combustion in alkanes?

A

In excess oxygen alkanes will burn with complete combustion.

The products of complete combustion are CO2 and H2O

19
Q

Write an equation of the complete combustion of C8H18 in an excess of oxygen.

A

(see page 2 in the chemrevise revision guide)

20
Q

What are the products of incomplete combustion in alkanes?

A

If there is a limited amount of oxygen then incomplete combustion occurs.

Producing CO (very toxic) and/or C (sooty flame)

21
Q

Write two of the equations for the incomplete combustion of CH4 in a limited amount of oxygen.

A

(see page 2 in the chemrevise revision guide)

22
Q

Give two negatives of the incomplete combustion.

A
  • Incomplete combustion produces less energy per mole than complete combustion.
  • Carbon (soot) can cause global dimming - reflection of the suns’s light.
23
Q

What is petroleum?

A

Petroleum is a mixture consisting mainly of alkane hydrocarbons.

24
Q

What is fractional distillation used for?

A

Fractional distillation is used to separate liquids with different boiling points.

25
Q

Draw a labelled diagram of the apparatus setup for fraction distillation in the laboratory.

A

(see page 1 in the chemrevise revision guide)

26
Q

Give 3 economic reasons for cracking.

A
  • The petroleum fractions with shorter C chains (e.g, petrol and naphtha) are in more demand than larger fractions.
  • To make use of excess larger hydrocarbons and to supply demand for shorter ones, longer hardocrabons are cracked.
  • The products of cracking are more valuable than the starting materials (e.g. ethene used to make poly(ethene), branches alkanes for motor fuels, etc.)
27
Q

What do Sulfur containing impurities produce when burned?

A

SO2

S + O -> SO2

CH3SH + O2 -> SO2 + CO2 + 2H2O

28
Q

What is the problem with SO2 in the atmosphere?

A

SO2 will dissolve in atmosphere water and can produce acid rain.

29
Q

Why do power stations produce lots of sulfur oxides?

A

Coal is high in sulfur content, and large amounts of sulfur oxides are emitted from power stations.

30
Q

How can SO2 be removed from the waste gases from furnaces (e.g. coal fired power stations)?

A

SO2 can be removed from the waste gases from furnaces (e.g. coal fired power stations) by flue gas desulfurisation. The gases pass through a scrubber containing basic calcium oxide which reacts with the acidic suffer dioxide in a neutralisation reaction.

SO2 + CaO -> CaSO3

The calcium sulphate formed can be used to make calcium sulfate for plasterboard.

31
Q

How are Nitrogen Oxides commonly formed?

A

Nitrogen oxides form from the reaction between N2 and O2 inside the car engine.

The temperature and spark in the engine provides sufficient engird to break strong N2 bond.

N2 + O2 -> 2NO

N2 + 2O2 -> 2NO2

32
Q

What are the environmental consequences of these pollutants:

  • Nitrogen oxides
  • Carbon monoxide
  • Carbon dioxide
  • Unburnt hydrocarbons
  • Soot
A

(see page 3 in the chemrevise revision guide)

33
Q

What do catalytic converters do?

A

Catalytic converters remove CO, nitrogen oxides, and unburned hydrocarbons (e.g. octane, C8H18) from the exhaust gases, turning them into ‘harmless’ CO2, N2 and H2O.

2CO + 2NO -> 2CO2 + N2
C8H18 + 25NO -> 8CO2 + 12.5N2 + 9H2O

Converters have a ceramic honeycomb coated with a thin layer of catalyst metals platinum, palladium, rhodium - to give a large surface area.

34
Q

Name 3 greenhouse gases, how do they affect the environment?

A

Greenhouse gases trap the Earth’s radiated infra red energy in the atmosphere.

  • Methane (CH4)
  • Water vapour (H2O)
    The main greenhouse gas (but its natural)
  • Carbon dioxide (CO2)
    The levels have risen significantly in recent years due to increasing burning of fossil fuels.
    Considered to be largely responsible for global warming.
35
Q

What are the 3 steps in free radical substitution?

A
  1. Initiation
  2. Propagation
  3. Termination
36
Q

What is the essential condition for free radical substitution?

A

UV light.

It supplies the energy to break the bond (e.g. Cl-Cl)

37
Q

What process of fission occurs in the initiation step of free radical substitution?

A

Homolytic fission.

38
Q

Draw all 3 free radical substitution steps for the reaction of methane with chlorine to produce chloromethane and HCl.

A

(see page 4 in the chemrevise revision guide)

39
Q

In general why do alkanes not react with many reagents?

A

In general, alkanes do not react with any reagents. This is because the C-C bond and the C-H bond are relatively strong.

40
Q

Write the mechanism of Br2 and propane. What is the essential condition of this reaction?

A

(see page 5 in the chemrevise revision guide)

41
Q

Write the overall equation for the formation of CCl4 from CH4 + Cl2

A

(see page 5 in the chemrevise revision guide)

42
Q

Write the overall equation for the formation of CFCl3 from CH3F + Cl2

A

(see page 5 in the chemrevise revision guide)

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