Alkanes And Petroleum Flashcards
(47 cards)
1
Q
Features of alkanes
A
- every carbon has 4 single bonds with another atom
- saturated
- cycloalkanes with 2 H attaches to it
2
Q
Steps of fractional distillation
A
1) crude oil heated in 350 degree to vaporised
2) then enter fractionating column, with negative temperature gradient (hottest at the bottom and coolest at the top)
3) then different hydrocarbons with different chain lengths and b.p. Condenses and Separated into different fractions with different b.p
4) the longer the chain= higher b.p = at the bottom, condense first
Shorter chain = low b.p so condense later or don’t condense stay in gas state
3
Q
Features of homologous series (4)
A
- same functional group and same general formula
- each differs by CH2
- gradual change in physical properties
- same chemical properties
4
Q
Definition of petroleum
A
- a mixture of straight and branched chain alkanes, cycloalkanes and sulfur impurities
5
Q
Trend of b.p of chain lengths
A
- longer the chains= higher b.p. = because stronger intermolecular forces as more VDW forces between electrons so need more energy to overcome the force
- shorter the chain= lower b.p as weaker VDW forces needed to break
6
Q
Trend of B.p of fractionating column
A
- bottom column as higher b.p. As needed to lose more energy to form back the bonds that once broke , form back gas to liquid
- top of column= need less energy to form back bonds as lower b.p
7
Q
Trend of b.p. On branching
A
- more branching = b.p decreases because irregular shape of branches causes molecules have fewer contact points of packing closely to each other = less VDW forces between molecules will form = easy to become gas
8
Q
Definition of cracking
A
- the process of breaking long chain alkanes into mixtures of shorter chain molecules such as alkenes, alkanes and hydrogen
9
Q
Purpose of cracking
A
- to turn longer chain alkanes that is not as useful and lower demand into shorter chain alkanes that is higher demand ass more useful
- so it is more economically valuable
10
Q
Benefits of cracking (3)
A
- increase economically valuable fractions (shorter chain )
- increase branching of alkanes = useful for petrol
- produce alkenes for making plastics
11
Q
Features of thermal cracking
A
- 400-900 degrees
- 7000kPa
- homolytic fission
- produce mostly Alkenes and hydrogen
- products uses for polymers to make plastics
12
Q
Features of catalytic cracking
A
- 450- 750 degree
- moderate pressure
- uses zeolite catalyst
- heterolytic fission
- produced branched and cyclic alkanes and aromatic hydrocarbons
- mostly added in fuels
13
Q
Pollutants in atmosphere
A
- carbon dioxide
- carbon monoxide
- unburnt hydrocarbons
- carbon soot
- sulfur dioxide
- nitrogen dioxide
14
Q
What is the effect of CO2 ?
A
- greenhouse gases, contributes to global warming and climate change
15
Q
How can CO2 be reduced ?
A
- reduce amount of hydrocarbons fuels burn
- use more efficient engines
- off set release by biofuels
16
Q
How does CO formed and its effect ?
A
- produced by incomplete combustion of hydrocarbons
- toxic gas = binds to haemoglobin and prevent O2 from binding, so oxygen cannot be carried around
17
Q
How can CO be reduced ?
A
- prevent incomplete combustion by providing sufficient O2
- use catalytic converters
18
Q
What is effect of unburnt hydrocarbons smoke ?
A
- contribution to formation of smog
19
Q
Effect of carbon soot
A
- cause global dimming and respiratory problems
20
Q
How does sulfur dioxide formed ?
A
- produced when burning fossil fuels contain sulfur, react with O2
21
Q
Effect of sulfur dioxide
A
- dissolves in water = form sulphuric acid = cause acid rain
22
Q
How to reduce sulfur dioxide ?
A
- flue gas desulfurisation
- powered calcium oxide dissolved in water then mix with flue gas = form calcium sulphite
SO2+ CaO -> CaSO3
23
Q
How is nitrogen oxide formed ?
A
- when high pressure and high temp in car engine cause nitrogen and oxygen to react
- the high level condition gives energy to break strong triple NN bond
24
Q
Effect and way to reduced nitrogen oxide
A
- toxic gas formed in car engines
- cause acid rain, respiratory problem
- use catalytic converters
25
What is catalytic converters ?
- a ceramic honeycomb structure coated by thin layer of catalytic metal which gives large SA
- use to convert CO and NO = to CO2, N2 and H2O
26
Describe greenhouse effect
- UV radiation by the sun is transmitted towards the earth’s atmosphere
- UV is absorbed by earth’s surface and re-emitted as infrared radiation
- greenhouse gases absorbed IR
- IR is re-emitted by greenhouse gases as cannot escape = warm up the surface of earth
27
How does CO2 causes global warming ? (3)
- C=O bond of + and - changes can move around easily due to vibration of particles
- this causes dipoles to change around = able to absorb IR
- the IR that is absorbed will transfer to other molecules by collision so most heat energy is trapped
28
Why is a thin layer of metal used inside a catalytic converter ?
M1 reduce amount of metals needed
M2 increase surface area so more gases can diffuse in/out quickly
29
Uses of haloalkanes
- more reactive than alkanes
- use for refrigerants, dry cleansing solvents
- have primary, secondary,tertiary haloalkanes
30
What is heterolytic fission ?
- when shared bond is broken and both shared electrons goes to one atom
- most common reaction
X—Y —> X+ + Y-
31
What is homolytic fission ?
- when shared bond is broken and each electron goes to each atom = making two free radicals
X. + Y.
32
What is a free radical ?
- they have an unpaired electron, don’t have a full outer shell= so it is very reactive as to react with other elements to get a full outer shell
33
Formula of free radical substitution of alkanes
Alkane + Halogen —> haloalkane + hydrogen-halide
E.g. CH4 + Cl2 —> CH3Cl + HCl
34
Process of free radical substitution
1) initiation : UV radiation uses to break the covalent bond that shared the pair of e- = making 2 free radicals e.g. Cl2–> Cl. + Cl.
2) propagation 1 : Cl. Attack the alkane CH4, so it lost one H = Cl. React with H = HCl
= .CH3 become a free radical
3) propagation 2 : .CH3 react with another Cl2= Cl. + CH3Cl
4) termination : always 2 free radicals react together (3 variations)
35
Variations of termination of FRS
1) .Cl + .CH3 —> ClCH3
2) .Cl + .Cl —> Cl2
3) .CH3 + .CH3 —> C2H6
36
Use of chlorofluorocarbons
- in refrigerants and solvents
37
What is the use of ozone layer
- to absorb harmful UV radiation (UVB+C)
- they can cause skin cancer
- form from O2 witch a free radical O
38
How does ozone layer break ?
- when UV breaks CFCs, leads to Cl. Forming that is harmful to stratosphere
- ozone layer breaks leads to UV B and C easier to direct into the earth = increase people’s risks of skin cancer
39
Trend of Carbon — halogen bond
- does down the group = bond strength decrease = easier to break
40
Conditions of nucleophilic sub of :OH- with a halogenoalkane
- aqueous condition
- heating under reflux
41
Conditions of nucleophilic sub of :CN- with a halogenoalkane
- ethanol/water mixture
- heating under reflux
42
Conditions of nucleophilic sub of NH3 with a halogenoalkane
- dissolved in ethanol
- heating under pressure in a sealed tube
43
Condition of elimination needs to be in
- halogenoalkanes + hot ethanoic solution of NaOH or KOH
44
Process of elimination
1) :OH- attacks one H atom on either side of C-X bond
2) causing the C-C to form a double bond into C=C
3) C-X bond break under heterolytic fission = causing a pair of electrons go to X
4) form :X- and alkene and H20
45
Process of Nucleophilic substitution
1) :Nu- lone pair of Nu attacks positive charge C in haloalkane
2) C-X bond breaks under heterolytic fission
3) Nu replace the X to form alcohol / amine / nitrile
4) results with replaced alkane and a halogen ion :X-
46
When to use elimination over N. Sub?
- tertiary structure haloalkane (preference over condition )
- NaOH/KOH in ethanoic condition
- higher temperature
47
When to use N.sub over elimination ?
- must be in primary haloalkane
- NaOH /KOH in aqueous condition
- warm temperature
