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Chemistry > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

What is the empirical formula?

A

Simplest whole number ratio

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2
Q

What is the molecular formula?

A

The actual number of atoms in a molecule

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3
Q

What is the structural formula?

A

Minimal detail of how the atoms are arranged in space
e.g. propane = CH3CH2CH3

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4
Q

What is the displayed formula?

A

Shows all the covalent bonds between every atom

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5
Q

What is the skeletal formula?

A

Carbon skeleton of a molecule where no hydrogen atoms are included
(Carbon atoms are represented by a dot and you don’t show hydrogen atoms)

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6
Q

What is the corresponding name beginning of each number?

A

One - meth
two - eth
three - prop
four - but
five - pent
six - hex
seven - hept
eight - oct
nine - non
ten - dec

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7
Q

What does the ending of an organic compound show?

A

The homologous series it is apart of

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8
Q

What are homologous series?

A

Families of organic compounds with the same functional group and same general formula

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9
Q

Do homologous series have the same chemical properties?

A

Yes

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10
Q

What does each member in a homologous series differ by?

A

CH2

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11
Q

What is the trend in physical properties of a homologous series?

A

There is a gradual trend - they have similar physical properties

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12
Q

What does it mean if something is saturated?

A

There are only single carbon bonds

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13
Q

What is a hydrocarbon?

A

A compound containing H and C

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14
Q

What is the general formula for alkanes?

A

CnH2n+2

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15
Q

How does fractional distillation work?

A
  • Crude oil is heated and vaporised
  • Fed into fractionating column
  • Gases rise up column
  • Condense at their boiling point
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16
Q

Which chains are at the bottom in fractional distillation and why?

A

The longer chains as they have a higher boiling point - more energy required to break London forces as there are more of them

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17
Q

Why are the longer chains at the bottom in fractional distillation less useful?

A

They are less flammable

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18
Q

What is cracking?

A

The breaking of large hydrocarbons into smaller hydrocarbons through breaking up carbon-carbon bonds

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19
Q

Why do we carry out cracking?

A
  • Shorter chains are more flammable
  • So more useful
  • So more in demand
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20
Q

When does complete combustion occur?

A

When we have sufficient oxygen - produces CO2 and H2O

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21
Q

When does incomplete combustion occur?

A

When we have insufficient oxygen - produces CO and H2O

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22
Q

List the pollutants

A

Carbon dioxide
Carbon monoxide
Particulates of carbon(soot)
Sulfur dioxide
Oxides of nitrogen

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23
Q

How is carbon dioxide formed and why is it harmful?

A
  • Formed in complete combustion
  • Contributes to global warming
24
Q

How is carbon monoxide formed and why is it harmful?

A
  • Incomplete combustion
  • Toxic gas
25
Q

How are particulates of carbon formed and why are they harmful?

A
  • Incomplete combustion
  • Found in chimneys, coal
  • Causes global dimming
  • Respiratory problems
26
Q

How is sulphur dioxide formed and why is it harmful?

A
  • Sulphur containing impurities in the fuel are burnt to form SO2
  • Acid rain - when it dissolves in atmospheric water vapour of liquid water, it is acidic
27
Q

How are oxides of nitrogen formed and why are they harmful?

A
  • N2 and O2 react at high temperatures in an engine to break the N-N bond
  • N2 and O2 come from the air or the atmosphere
  • Acid rain
    Respiratory problems
28
Q

Why is more energy required to break up N2 than O2?

A

N2 has triple covalent bonds

29
Q

What does a catalytic converter do?

A

Converts CO, NOx and unburned fuels to N2, CO2 and water vapour

30
Q

What is the catalyst in a catalytic converter made from?

A

Either:
- Platinum
- Rhodium
- Palladium

31
Q

What shape is the catalyst in a catalytic converter in?

A

A honeycomb to increase surface area to increase rate of reaction (known as catalysis)

32
Q

Why do we use alternative fuels?

A

To reduce pollution

33
Q

What kind of fuel are biofuels?

A
  • Renewable fuels
  • They can be replaced over a short period of time
  • The bio part means it comes from living matter
34
Q

What are the 3 main biofuels and how are they made?

A

Biodiesel - made by refining renewable fats and oils

Bioethanol - made by fermentation

Biogas - made/released when organic waste breaks down

35
Q

What are biofuels often considered as?

A

Carbon neutral

36
Q

What does carbon neutral mean (link to biofuels)?

A
  • As plants grow, absorb CO2 which is = amount of CO2 they release when burnt
  • Not completely true as CO2 will be produced in refining and transport of plants
37
Q

What do biodiesel and biofuel do?

A

Reduce the amount of waste going to landfill

38
Q

How do biodiesel and biofuel reduce the amount of waste going to landfill?

A

The waste can be used to produce them

39
Q

How could biofuel production provide money for less developed countries?

A

They have space to grow the crops required

40
Q

What is a disadvantage of biofuels in terms of cost?

A

The cost of converting engines and machinery to run on biofuels instead of petrol/diesel

41
Q

What is a disadvantage of biofuels in conjunction with developed countries?

A

Many developed countries don’t have space to be able to produce enough plants to make the biofuels as land is needed for food production

42
Q

What is reforming?

A

It is the process of turning straight chain hydrocarbons into branched-chain alkanes and cyclic hydrocarbons

43
Q

Why are cyclic hydrocarbons more useful?

A

They are used for more efficient combustion

44
Q

What is free radical substitution?

A

Replacing H atoms with halogen atoms

45
Q

How do we carry out free radical substitution?

A

We react halogens with UV light

46
Q

What do we form in free radical substitution?

A

Halogenoalkanes

47
Q

What are free radicals and what is their reactivity like?

A

Free radicals have an odd number of electrons
They are very reactive

48
Q

How do we represent free radicals?

A

It is drawn as a . on the atom with the odd number of electrons

49
Q

What are the 3 steps to free radical substitution?

A

Initiation
Propagation
Termination

50
Q

What is initiation?

A

It involves the splitting of the halogen bond using UV light (e.g. splitting of Cl-Cl)

51
Q

What is propagation?

A
  • The halogen free radicals produced are extremely reactive
  • In the propagation step a free radical reacts with a reactant and produces a molecule and another free radical
52
Q

What is termination?

A

When any 2 free radicals meet they react to form a molecule
This removes free radicals and stops the chain reaction

53
Q

What is formed in free radical substitution?

A

Alkane + halogen = halogenoalkane + H-X

54
Q

What is the definition of a free radical substitution?

A

A reactive species that has an unpaired electron

55
Q

What is 1 limitation of free radial substitution?

A

Impurities - multiple termination steps

56
Q

What is another limitation of free radical substitution?

A

Further substitutions - more than 1 halogen is substituted onto a C

57
Q

What is another limitation of free radical substitutuion?

A

Substitution of different C atoms
- Halogen substituted onto different C atoms

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