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AS Chemistry - Unit 1 > Unit 3.1.6 - Alkanes > Flashcards

Unit 3.1.6 - Alkanes Flashcards

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1
Q

What are alkanes?

A

Saturated hydrocarbons

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2
Q

What is meant by alkanes being saturated?

A

They only have single bonds between all the carbon atoms

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3
Q

What is a hydrocarbon?

A

A substance containing only carbon hydrogen atoms

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4
Q

What is crude oil a mixture of?

A

Different length hydrocarbons

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5
Q

What process is used to split crude oil up into its different fractions?

A

Fractional distillation

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6
Q

Describe the 4 steps in fractional distillation that spilt crude oil up into its different fractions?

A
  1. ) Crude oil is vaporised at about 350oC
  2. ) Passed through a fractionating column
  3. ) The boiling point of each fraction is different depending on the length of the chain
  4. ) Because of the temperature gradient in the column, each fraction is tapped of at the point that it condenses
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7
Q

What is the temperature gradient of a fractionating column?

A

The temperature decreases as you go up the column

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8
Q

Do longer of shorter chain hydrocarbons have a higher boiling point?

A

Longer

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9
Q

Why do longer hydrocarbon chains have the highest boiling point

A

There are a greater number of carbon atoms in the chain so more Van der Waal’s forces acting between the molecules which require more energy to overcome

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10
Q

What is a fraction?

A

A mixture of hydrocarbons with similar boiling points

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11
Q

Name one use of the residue which is tapped out of the bottom of a fractionating column?

A

Lubricating oil

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12
Q

Name one use of the shorter chain fractions?

A

Petrol for in cars

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13
Q

Is there a higher or smaller demand for shorter chain hydrocarbons compared to longer chain hydrocarbons?

A

Higher demand

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14
Q

Is there a bigger supply of the smaller or longer chain hydrocarbons?

A

Longer

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15
Q

As there is a small supply for the high demand shorter chain hydrocarbons how do they meet the demand?

A

The longer chains go through the process of cracking

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16
Q

Give two reasons why cracking is important?

A
  1. ) converts low demand fractions into higher demand fractions
  2. ) it makes useful hydrocarbons not naturally found in crude oil
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17
Q

What is cracking?

A

The breaking of C-C bonds to form smaller molecules

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18
Q

What are the names of the two types of cracking?

A

Thermal and catalytic

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19
Q

What are the conditions of thermal cracking?

A 
High temperature (400-900oC)
High pressure (70 atm)
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20
Q

What does thermal cracking mainly produce?

A

Alkenes

21
Q

What are the conditions of catalytic cracking?

A 
High temperature (450oC)
Slight pressure (a bit bigger than 1 atm)
Zeolite catalyst
22
Q

Does thermal or catalytic cracking involve using a catalyst? and what is the name of the catalyst?

A

Catalytic - zeolite

23
Q

What does catalytic mainly produce?

A

Motor fuels and aromatic hydrocarbons

24
Q

Is thermal or catalytic cracking cheaper and more efficient and why?

A

Catalytic - it uses lower a temperature and pressure

25
Q

Why are alkanes good to use as fuels?

A

They produce a large amount of energy from a small amount of fuel

26
Q

What is complete combustion?

A

When you burn a fuel fully in a lot of oxygen

27
Q

What are the products of complete combustion?

A

Water and carbon dioxide

28
Q

What is the equation for the complete combustion of propane?

A

C3H8 + 5O2 ———-> 3CO2 + 4H20

29
Q

What happens if you burn a fuel in not enough oxygen?

A

Incomplete combustion

30
Q

What can the products of incomplete combustion be?

A

Carbon monoxide, carbon, carbon dioxide and water

31
Q

What are three reasons why incomplete combustion is bad?

A
  1. ) It releases less energy than complete combustion
  2. ) Carbon particles can cause breathing difficulties and cancer
  3. ) Carbon monoxide is poisonous and is absorbed into the blood instead of oxygen
32
Q

In an engine why do does the nitrogen and oxygen in the air sometime react?

A

Because of the higher temperatures and pressure in the engine

33
Q

What are the two equations for when nitrogen reacts with oxygen in the air when in an engine?

A

N2 + O2 ———-> 2NO

2NO + O2 ———-> 2NO2

34
Q

Why is nitrogen dioxide bad?

A

It dissolves in rainwater to form an acidic solution and cause acidic rain

35
Q

Why are nitrogen oxides bad?

A

They can combine with unburnt hydrocarbons to produce photochemical smog

36
Q

What are catalytic converters used for?

A

To remove harmful unburned hydrocarbons

37
Q

What two substances can be removed by catalytic converters?

A

Carbon monoxide and oxides of nitrogen

38
Q

What is the equation for how carbon monoxide can be removed by catalytic converters?

A

2NO + 2CO ———-> N2 + 2CO2

39
Q

What is the equation for how oxides of nitrogen can be removed by catalytic converters

A

2NO ———-> N2 + O2

40
Q

Name two transition metals used in catalytic converters?

A

Platinum and iridium

41
Q

What impurity does most crude oil contain?

A

Sulphur

42
Q

What is the equation for when sulphur impurities are burnt in the air?

A

S + O2 ———-> SO2

43
Q

Why is sulphur dioxide bad?

A

It can dissolve in rain water like nitrogen dioxide and form an acidic solution causing acidic rain

44
Q

How do factories prevent sulphur dioxide from escaping?

A

They use flue gas desulphurization

45
Q

How does flue gas desulphurization prevent sulphur dioxide from escaping?

A

They contain alkaline materials like calcium oxide which neutralise the sulphur dioxide gases

46
Q

What is the equation for when sulphur dioxide reacts during flue gas desulphurization?

A

CaO + SO2 ———-> CaS03

47
Q

What are gases that contribute to global warming called?

A

Greenhouse gases

48
Q

What are five example of greenhouse gases?

A
  1. ) Carbon dioxide
  2. ) Water vapour
  3. ) Carbon monoxide
  4. ) Carbon
  5. ) Methane
49
Q

How do greenhouse gases contribute to global warming?

A

Electromagnetic radiation from the sun reaches the earth and some of it is absorbed, the earth then re emits it as infrared radiation
Greenhouse gases absorb this radiation and re emit it in all directions, including back towards earth
This causes the temperature to rise and so global warming to happen

AS Chemistry - Unit 1 (7 decks)

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