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Topic 6: Organic chemistry 1 > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

What is the general formula for alkanes ?

A

CnH2n + 2

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2
Q

What does it mean if the alkanes are hydrocarbons ?

A

they contain hydrogen and carbon atoms only

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3
Q

Two types of hydrocarbons

A

aliphatic and aromatic hydrocarbons

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4
Q

aliphatic hydrocarbons

A

chains of carbon atoms which may be branched or unbranched and with rings that are not aromatic

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5
Q

aromatic hydrocarbons

A

rings in which there are delocalised electrons - named because of their smells - sometimes called arenes

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6
Q

Saturated compunds

A

only single bonds between the atoms in their molecules

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7
Q

Where are alkanes found ? - fractional distillation

A

alkanes are found in crude oil which is a mixture of different length hydrocarbons

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8
Q

Fractional Distillation

A
  • vaporised oil enters the column and rises through the trays
  • the longest hydrocarbons don’t vaporise and run down to the bottom
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9
Q

What does the column in fractional distillation have ?

A

It has a temperature gradient
- cooler at the top
- as the vapour rises parts of the mixture condense at different temperatures - because there are different chain lengths and hence different boiling points
- the fractions are drawn off at different levels

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10
Q

What happens to the shortest hydrocarbons ?

A

they won’t even condense at 20 degrees Celsius and so comes off as a gas at the top of the column

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11
Q

How can the fractions be used ?

A

gas - used in LPG and stove gas
petrol - used in petrol cars
kerosine - used as jet fuel and heating
diesel oil - used in diesel oil
fuel oil - used in ships and power stations
bitumen - used in roofing and tarmac

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12
Q

Cracking

A

heavier fractions can be cracked to higher demand lighter fractions

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13
Q

What does fractional distillation produce ?

A

it produces a variety of fractions however demand for each fraction varies

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14
Q

Is heavier fractions like fuel oil higher or lower demand ?

A

Lower demand than lighter fractions such petrol which are more valuable

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15
Q

What are the two types of cracking ?

A

thermal and catalytic cracking

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16
Q

Thermal cracking

A
  • high temperatures and pressure used in 10000 degrees celcius
  • 70 atm of pressure
  • products = alkenes
  • alkenes are used to make polymers such as plastics
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17
Q

Catalytic cracking

A
  • high temperature and slight pressure used 450 degrees celcius
  • a zeolite is used which helps to lower the temperature needed
  • products = aromatic hydrocarbons useful in fuel in vehicles
  • using a zeolite cataylst lowers the temperature and pressure needed for cracking to occur - lowers costs and speeds up process
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18
Q

Reforming alkanes

A

alkanes can be reformed into cycloalkanes and aromatic molecules

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19
Q

What are petrol and diesel made up of ?

A

a mixture of hydrocarbons some of which are straight chain hydrocarbons

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20
Q

What is the problem with straight chain alkanes ?

A

create knocking in car engine - knocking is where straight chain alkanes explode upon compression
- adding branched and cyclic alkanes reduces knocking and increases engine efficiency

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21
Q

How can cyclic and branched alkanes be made ?

A

by using straight chain alkanes and a platinum in a process called reforming

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22
Q

Complete combustion of alkanes

A
  • alkanes burn in oxygen completely to form carbon dioxide and water
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23
Q

Why are alkanes good fuels ?

A

they burn readily to produce large amount of energy - the longer the alkane the more energy they produce

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24
Q

What is the combustion of alkanes used for ?

A

power vehicles and most of Britain’s electricity

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25
Q

Incomplete combustion of alkanes

A

when alkanes burn with a limited oxygen supply we produce carbon monoxide and carbon (soot)

26
Q

How is carbon monoxide poisonous ?

A

bonds to haemoglobin in the blood and prevents oxygen bonding - can be removed using catalytic converter

27
Q

What can soot cause ?

A

causes breathing problems and make up building dirty and clog up engines

28
Q

Acid rain

A

burning fossil fuels can release sulfur dioxide and oxides of nitrogen which contribute to acid rain

29
Q

What does acid rain cause ?

A

damage to plants, kills fish and causes erosion of buildings

30
Q

Some fossil fuels contain sulfur based impurities …

A

when burned the sulfur reacts with oxygen producing sulfur dioxide

31
Q

What is sulfur dioxide ?

A
  • an acidic gas
  • reacts with water in the atmosphere to form sulfuric acid which falls as acid rain
32
Q

Oxides of nitrogen

A
  • these are produced when nitrogen and oxygen are heated in the engine and react
  • dissolve in water in the atmosphere to form nitric acid when contributes to acid rain
33
Q

Where are catalytic converter found ?

A

they are found mainly in vehicles and help to reduce harmful pollutants entering the atmosphere

34
Q

What does catalytic converter help to reduce ?

A

the amount of unburnt hydrocarbons and oxides of nitrogen going into the atmosphere

35
Q

What does catalytic converter contain ?

A

platinum, rhodium and indium metals

36
Q

What do catalytic converter convert ?

A

they convert harmful gases like :
- carbon monoxide
- oxides of nitrogen
- unburnt hydrocarbons
into less harmful products like
- water vapour
- nitrogen
- carbon dioxide

37
Q

What are fossil fuels ?

A

created from dead animals and plants that lived millions of years ago

38
Q

Is fossil fuels renewable or non - renewable ?

A

non - renewable ( will run out ) and manily include :
- coal
- gas
- oil

39
Q

Can fossil fuels run out ?

A

Fossil fuels will run out. Oil in particular is in a short supply and is becoming increasingly more difficult to extract. This means the cost of extraction increases too.

40
Q

Coal, gas and oil can be …

A

extracted easily and are a good source of energy as a fuel

41
Q

Biofuels

A

adv -biofules are renewable so they are a more sustainable than crude oil
- produce CO2 when they are burnt however they are classes as carbon neutral as the CO2 is absorbed by the plants when its growing
dis - expensive to convert existing petrol engines to take fuels with higher concentration of ethanol
- land that could have been used to grow food is being used to make food shortages in countries that grow sugar cane

42
Q

what are the two types of chemical reactions of alkanes ?

A

combustion ( complete and incomplete )
free radical subsistution

43
Q

free radical

A

a chemical species with an unpaired electron

44
Q

substitution

A

a reaction in which one atom is replaced by another atom or group

45
Q

what do mechanisms show ?

A

the movement of electrons and bonds that allow reactant to change into products

46
Q

arrows will always travel ..

A

from negative to postitive when forming a bond

47
Q

what does a double headed arrow represent ?

A

2 electrons moving

48
Q

what does a single headed ( fish hook ) represent ?

A

1 electron moving

49
Q

what are the two types of bond fission ?

A

homolytic and heterolytic

50
Q

bond fission

A

the breaking of a covalent bond. the electron pair in the bond can be distributed into 2 ways

51
Q

Heterolytic fission

A

the bond breaks but the electrons are distributed unequally to form 2 different ions ( an anion and anion )

52
Q

what does hetero mean ?

A

different

53
Q

Homolytic fission

A

the bond breaks with the pair of electrons in the bond being shared equally to form 2 uncharged radicals

54
Q

what does the dot mean ?

A

there is an unpaired electron on the atom

55
Q

what does homo mean ?

A

same

56
Q

state the 3 main stages in chain reactions

A

initiation
propagation
termination

57
Q

initiation

A

radicals are produced normally using visible light or ultra violet - called photochemical reactions.
the bond breaks producing 2 radicals

58
Q

Propagation

A

when a radical reacts with a non radical molecule. New radicals are created which then go to react with other non-radicals - chain reaction

59
Q

Termination

A

when 2 radicals react they form a non-radical molecule - ends the chain reaction

60
Q

If there is loads of chlorine in the reaction we will get ..

A

di, tri, tetra haloalkane

61
Q

By adding excess methane it will ..

A

reduce the amount of multiple substitutions - greater chance of chlorine reacting with methane

62
Q

Ina addition to multiple substitution what else would form ?

A

isomers - because free radical substitution will occur anywhere on a hydrocarbon chain

Topic 6: Organic chemistry 1 (7 decks)

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