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Chemistry AS Level > Organic 1: Alkanes > Flashcards

Organic 1: Alkanes Flashcards

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1
Q

what is an alkane

A

a saturated hydrocarbon

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2
Q

what is the general formula of an alkane?

A

Cn H2n+2

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3
Q

are the bonds in alkanes polar?

A

non-polar

carbon and hydrogen have similar electronegativities

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4
Q

what intermolecular forces are in alkanes and why

A

only van der waals - bonds are non-polar

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5
Q

are alkanes soluble in water

A

insoluble because hydrogen bonds in water are stronger than alkanes’ van der waals forces of attraction

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6
Q

how reactive are alkanes

A

very unreactive

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7
Q

which reactions will alkanes undergo

A

combustion and reaction with halogens

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8
Q

what is crude oil? how is it formed? is it renewable? why?

A
  • mixture of fractions (hydrocarbons with similar boiling points and properties)
  • formed at high temperatures and pressures deep below earth’s surface over millions of years
  • non renewable
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9
Q

name the fractions from high to low boiling point

A
  1. gases
  2. gasoline/petrol/naphtha
  3. kerosene/paraffin
  4. diesel oil
  5. lubricating oil/waxes
  6. fuel oil
  7. tar/bitumen
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10
Q

what is fractional distillation and how does it work?

A
  • crude oil is heated until mostly vaporised
  • passed into a fractionating tower that is cooler at the tip than the bottom
  • liquid fractions are piped off at the bottom
  • vapours rise up the column and (via trays and bubble caps) condense when the temperature is lower than their boiling point
  • shortest chain hydrocarbons condense at the top as they have the lowest boiling points
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11
Q

what is fracking and how is it done?

A
  • natural gas in shale rock
  • drill into shale, force pressurised water and sand into rock to fracture it, collect gas
  • HCl and methanol added to break up shale and prevent corrosion
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12
Q

advantages and disadvantages of fracking?

A 
advantages :
 - gas supply for many years 
 - reduces imported gas and electricity 
disadvantages :
 - lots of traffic to local area 
 - concern about amount of water used 
 - chemical additives can pollute water supplies 
 - can cause small earthquakes 
- combust CH4 --> CO2 
- global warming
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13
Q

why are alkanes cracked?

A

to turn a long chain alkane, which is not very economically valuable, into a shorter chain alkane (more economically valuable because it can be used as a fuel) and an alkane (more reactive starting point for many products)

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14
Q

what are the conditions for thermal cracking?

A

700-1200K temperature

UP to 7000 kPa pressure

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15
Q

what is the intermediate for the reaction

A

free radicals

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16
Q

what are the main products of thermal cracking

A

alkenes

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17
Q

what are the conditions for catalytic cracking

A

lower temp - 720K
lower pressure but above atmospheric
zeolite catalyst (SiO2 and Al2O3) with a honeycomb structure to give a large surface area

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18
Q

what are the main products of catalytic cracking

A

cycloalkanes
aromatic hydrocarbons
branched alkanes

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19
Q

an equation for the combustion of propane

A

C3H8 + 5O2 –> 3CO2 + 4H2O

20
Q

what is a fuel

A

something which releases heat energy when combusted

21
Q

what are the five main fuels comprising of alkanes

A 
methane
butane 
propane 
petrol (about C8) 
paraffin (C10 - C18)
22
Q

what is incomplete combustion and what products are formed in the case of alkanes

A

combustion in a limited supply of oxygen
CO - carbon monoxide - poisonous
C - carbon - particulates - soot - global dimming

23
Q

which type of hydrocarbons are most likely to undergo incomplete combustion?

A

longer chains

24
Q

what is the environmental impact of carbon monoxide

A

toxic/poisonous

25
Q

what is the environmental impact of nitrogen oxides

A

form nitric acid - acid rain, photochemical smog

26
Q

what is the environmental impact of sulfur impurities/sulfur dioxide

A

form sulphuric acid –> acid rain

27
Q

what is the environmental impact of soot

A

asthma
cancer
global dimming

28
Q

what is the environmental impact of unburnt hydrocarbons

A

photochemical smog

29
Q

what is the environmental impact of carbon dioxide

A

greenhouse gas mean global warming

increasing global temperatures speeds up climate change

30
Q

what is the environmental impact of water vapour

A

greenhouse gas - global warming

increases global temperatures therefore speeds up climate change

31
Q

what are flue gases

A

gases given out by power stations

32
Q

write two equations for two different ways of desulfurising flue gases

A

CaO(s)+2H2O(l)+SO2(g)+1/2O2(g)–> CaSO4.2H2O(s)

or

CaCO3(s)+SO2(g)+1/2O2(g)–> CaSO4+CO2(g)

33
Q

what are catalytic converters made up of

A

ceramic honeycomb coated with platinum, palladium and rhodium metals

34
Q

what do catalytic converters catalyse (include equations)

A

catalyse products from car exhausts
2CO(g) + 2NO(g) –> N2(g) + 2CO2(g)

hydrocarbons+NO–> N2 + CO2 + H2O

35
Q

what are greenhouse gases

A

gases which trap infrared radiation, making the earth act like a greenhouse

36
Q

what is the greenhouse effect and how does it contribute to global warming

A

greenhouse gases trap infrared radiation in the atmosphere, atmosphere heats up –> global warming

37
Q

define carbon neutral activities

A

activities that produce no net carbon dioxide emissions

38
Q

how are halogenoalkanes formed from alkanes

A

free radical substitution reaction

39
Q

what are the three stages of free radical substitution?

A
  1. initiation - breaking halogen bond to form free radicals
  2. propagation - chain part of the reaction where products are formed but free radical remains
  3. termination - free radicals removed, stable products formed
40
Q

what are the conditions needed for the formation of a free radical chlorine atom?

A

presence of UV light

41
Q

write equation for the reaction of CH4 with Cl2 to form CH3Cl

A 
initiation - 
Cl2 --> 2Cl
propagation 
Cl + CH4 -->HCl + CH3 
CH3 + Cl2 --> CH3Cl + Cl 
termination 
CH3 + Cl --> CH3Cl 
2Cl -->Cl2
CH3 + CH3 --> CH3CH3
42
Q

what is the function of the ozone layer

A

protects the earth from harmful exposure to too many UV rays

43
Q

how do CFCs break the ozone layer down

A

free radical substitution

44
Q

write an equation for the overall decomposition of ozone into oxygen (o2)

A

2O3 –> 3O2

45
Q

write the free radical substitution equations to show how Cl free radicals catalyse the decomposition of O3

A

Cl2 –> 2Cl (in presence of UV light)
Cl + O3 –> ClO + O2
ClO + O3 –> 2O2 + C

overall: 2O3 –> 3O2

Chemistry AS Level (18 decks)

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