Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Topic 6: Organic chemistry 1 > Alkanes > Flashcards

Alkanes Flashcards

(62 cards)

Start Studying
1
Q

What is the general formula for alkanes ?

A

CnH2n + 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does it mean if the alkanes are hydrocarbons ?

A

they contain hydrogen and carbon atoms only

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Two types of hydrocarbons

A

aliphatic and aromatic hydrocarbons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

aliphatic hydrocarbons

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

aromatic hydrocarbons

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Saturated compunds

A

only single bonds between the atoms in their molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Where are alkanes found ? - fractional distillation

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Cracking

A

heavier fractions can be cracked to higher demand lighter fractions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does fractional distillation produce ?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Is heavier fractions like fuel oil higher or lower demand ?

A

Lower demand than lighter fractions such petrol which are more valuable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the two types of cracking ?

A

thermal and catalytic cracking

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Reforming alkanes

A

alkanes can be reformed into cycloalkanes and aromatic molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are petrol and diesel made up of ?

A

a mixture of hydrocarbons some of which are straight chain hydrocarbons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How can cyclic and branched alkanes be made ?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Complete combustion of alkanes

A
  • alkanes burn in oxygen completely to form carbon dioxide and water
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the combustion of alkanes used for ?

A

power vehicles and most of Britain’s electricity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Incomplete combustion of alkanes
when alkanes burn with a limited oxygen supply we produce carbon monoxide and carbon (soot)
26
How is carbon monoxide poisonous ?
bonds to haemoglobin in the blood and prevents oxygen bonding - can be removed using catalytic converter
27
What can soot cause ?
causes breathing problems and make up building dirty and clog up engines
28
Acid rain
burning fossil fuels can release sulfur dioxide and oxides of nitrogen which contribute to acid rain
29
What does acid rain cause ?
damage to plants, kills fish and causes erosion of buildings
30
Some fossil fuels contain sulfur based impurities ...
when burned the sulfur reacts with oxygen producing sulfur dioxide
31
What is sulfur dioxide ?
- an acidic gas - reacts with water in the atmosphere to form sulfuric acid which falls as acid rain
32
Oxides of nitrogen
- 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
Where are catalytic converter found ?
they are found mainly in vehicles and help to reduce harmful pollutants entering the atmosphere
34
What does catalytic converter help to reduce ?
the amount of unburnt hydrocarbons and oxides of nitrogen going into the atmosphere
35
What does catalytic converter contain ?
platinum, rhodium and indium metals
36
What do catalytic converter convert ?
they convert harmful gases like : - carbon monoxide - oxides of nitrogen - unburnt hydrocarbons into less harmful products like - water vapour - nitrogen - carbon dioxide
37
What are fossil fuels ?
created from dead animals and plants that lived millions of years ago
38
Is fossil fuels renewable or non - renewable ?
non - renewable ( will run out ) and manily include : - coal - gas - oil
39
Can fossil fuels run out ?
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
Coal, gas and oil can be ...
extracted easily and are a good source of energy as a fuel
41
Biofuels
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
what are the two types of chemical reactions of alkanes ?
combustion ( complete and incomplete ) free radical subsistution
43
free radical
a chemical species with an unpaired electron
44
substitution
a reaction in which one atom is replaced by another atom or group
45
what do mechanisms show ?
the movement of electrons and bonds that allow reactant to change into products
46
arrows will always travel ..
from negative to postitive when forming a bond
47
what does a double headed arrow represent ?
2 electrons moving
48
what does a single headed ( fish hook ) represent ?
1 electron moving
49
what are the two types of bond fission ?
homolytic and heterolytic
50
bond fission
the breaking of a covalent bond. the electron pair in the bond can be distributed into 2 ways
51
Heterolytic fission
the bond breaks but the electrons are distributed unequally to form 2 different ions ( an anion and anion )
52
what does hetero mean ?
different
53
Homolytic fission
the bond breaks with the pair of electrons in the bond being shared equally to form 2 uncharged radicals
54
what does the dot mean ?
there is an unpaired electron on the atom
55
what does homo mean ?
same
56
state the 3 main stages in chain reactions
initiation propagation termination
57
initiation
radicals are produced normally using visible light or ultra violet - called photochemical reactions. the bond breaks producing 2 radicals
58
Propagation
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
Termination
when 2 radicals react they form a non-radical molecule - ends the chain reaction
60
If there is loads of chlorine in the reaction we will get ..
di, tri, tetra haloalkane
61
By adding excess methane it will ..
reduce the amount of multiple substitutions - greater chance of chlorine reacting with methane
62
Ina addition to multiple substitution what else would form ?
isomers - because free radical substitution will occur anywhere on a hydrocarbon chain

Topic 6: Organic chemistry 1 (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions