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Chemistry Y12 > O- Alkanes > Flashcards

O- Alkanes Flashcards

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1
Q

What is the main source of alkanes?

A

crude oil

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2
Q

Uses of alkanes

A
  1. fuels
  2. lubricants
  3. starting materials for other compounds
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3
Q

Bond angle of straight chain alkanes

A

109.5

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4
Q

General formula for cyclic alkanes

A

CnH2n
** cyclic isomers to alkenes

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5
Q

Polarity

A

non-polar
∵ C & H - similar electronegativities

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6
Q

Boiling points

A
  • longer chain ↑ bp
    –↑ vdW BETWEEN MOLECULES
  • straight chain ↑ bp
    –√ packed ↑ tightly tgt–> ↑ vdW
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7
Q

Solubility

A
  • insoluble
    – strong H bonds in water, stronger than vdW between alkanes (↑ stable- x break to form vdW to mix)
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8
Q

Reactivity

A
  • unreactive ∵ strong C-C & C-H bonds
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9
Q

3 conditions for crude oil to form

A
  1. ↑↑ heat & pressure
  2. millions of years
  3. biomass (eg. plants & animals)
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10
Q

What is crude oil?

A

Mixture of diff. (branched & unbranched) alkanes of diff. lengths

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11
Q

What is a fraction?

A

Group of alkanes w/ similar chain lengths & bp

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12
Q

What is bitumen used for?

A
  1. road surfacing
  2. further processed
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13
Q

What are alkenes from fractional distillation used for?

A
  1. polymers
  2. starting materials for other compounds
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14
Q

2 types of cracking

A
  1. thermal
  2. catalytic
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15
Q

Conditions for thermal cracking

A
  1. high temp- {700-1200K}
  2. high pressure- {7000kPa}
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16
Q

Describe how each type of products are formed in thermal cracking.

A

bond between 2 carbons in hydrocarbon chain splits into 2 molecules each w/ a free radical (unbonded e-)

Alkanes:
- free radical reacts w/ H –> alkane

Alkenes:
- x enough H –> loses 1 H–> alkene

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17
Q

Conditions for catalytic cracking

A
  1. lower temp- {720K}
  2. ↓ pressure
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18
Q

What is a zeolite catalyst + how is it adapted for its function?

A
  • silicon dioxide + aluminium oxide
  • honeycomb structure w/ ↑ s.a.
  • acidic
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19
Q

Types of products formed in catalytic cracking

A
  1. branched alkanes
  2. cyclic alkanes
  3. aromatics
20
Q

What is the effect of no. of carbons in the amount of energy released in complete combustion?

A

↑ no. of carbons ↑ heat energy released

21
Q

Products of incomplete combustion

A
  1. CO
  2. carbon particulates (soot)
22
Q

As the chain length increases, what happens to the likelihood of incomplete combustion?

A

↑
∵ ↑ carbons require ↑ O2 for complete combustion

23
Q

How are Nitrogen oxides (NO, NO2, N2O4) formed?

What are the negative consequences?

A
  • nitrogen & O2 from atmosphere react
  • high temp
  • ✔ react w/ water vapour & O2 in air–> nitric acid
    – 1. photochemical smog
    – 2. acid rain
24
Q

Negative consequences for CO

A
  • toxic
  • haemoglobin has a high affinity for it
25
Q

Negative consequences for carbon particulates

A
  • cancer
  • exacerbate asthma
26
Q

Negative consequences of unburnt hydrocarbons

A
  • photochemical smog
27
Q

Negative consequence of SO2

A
  • sulfur in fossil fuels–> SO2
    – reacts w/ O2 & H2O in atmosphere –> sulfuric acid–> acid rain

SO2 (g)+ 1/2 O2 (g) + H2O (l) –> H2SO4 (l)

28
Q

How is SO2 formed?

A
  • sulfur-containing impurities in crude oil
  • sulfur in fossil fuels
29
Q

What is flue gas?

A

Fossil fuels burnt at power stations

30
Q

Describe how flue gas desulfurization is carried out

A
  • 2 methods
    1. spray slurry of lime (CaO) & water on flue gas
    — SO2 forms calcium sulphite–> oxidised–> calcium sulfate (gypsum)
  • sold to make builder’s plaster/ plasterboard

CaO (s) + 2H2O (l) + SO2 (g) + ½ O2 (g) –> CaSO4.2H2O (s)

  1. calcium carbonate xlime

CaCO3 (s) + ½ O2 (g) + SO2 (g) –> CaSO4 (s) + CO2 (g)

31
Q

What does flue gas desulfurization get rid of?

A

sulfur dioxide

32
Q

What do catalytic converters get rid of?

A
  • nitrogen oxides
  • carbon monoxide
  • unreacted hydrocarbons
33
Q

Describe what a catalytic converter is made of

A
  • honeycomb structure
  • ceramic material
  • expensive metals eg. platinum & rhodium
34
Q

Important feature of a catalytic converter

A

↑ s.a.
↓ amount of metals for same effect

35
Q

Chemical equation for removal of carbon monoxide

A

2CO (g) + 2NO (g)  N2 (g) + 2CO2 (g)

36
Q

Word equation for removal of unburnt hydrocarbons

A

Unreacted hydrocarbons + nitrogen oxide  nitrogen + carbon dioxide + water

37
Q

What is carbon neutrality?

A
  • process/ activities that release no CO2 emissions overall
38
Q

What is the reaction forming a halogenoalkane called and what is the condition?

A
  • substitution reaction- H substituted by halogen
  • condition- UV light
39
Q

3 steps in free radical substitution

A
  1. initiation- halogen absorbs a single quantum of UV light
  2. propagation- the chain part (repeats)
  3. termination- getting rid of radicals
40
Q

Product of initiation

A

2 radicals
eg. 2Cl.

41
Q

Why do C-H bonds not break under UV light?

A

wrong wavelength- only breaks bonds between halogens

42
Q

Products of each step in propagation

A

eg. reacting Cl w/ methane (CH4)
1. CH3 radical
2. Cl radical
– both reactants for the other reactions–> repeating chain

43
Q

Why are chain reactions not selective?

A
  • any product can be formed
  • ∵ any C-H bond could be broken in alkane
    –> positional isomers
44
Q

List the 3 possible products in termination

A

👑 1. halogenoalkane
2. halogen
3. bigger alkane

45
Q

Why is a hole in the ozone (O3) layer a problem?

A
  • harmful UV radiation from the sun goes through the hole
  • sunburn + skin cancer

Chemistry Y12 (33 decks)

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