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Chemistry old > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

alkanes are?

A

saturated hydrocarbons

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2
Q

what is petroleum?

A

crude oil; mixture consisting of alkane hydrocarbons that can be separated by fractional distillation

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3
Q

what is crude oil?

A

fossil fuel made from breakdown of plant and animal remains subjected to high pressure over millions of years

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4
Q

why are alkanes non polar

A

electronegativaties of hydrogen and carbon are so similar

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5
Q

forces between alkanes

A

VDW

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6
Q

why do alkanes with branched chains have lower boiling points than unbranched ones w/ the same number of hydrocarbons

A

cannot pack closely together- weaker VDW

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7
Q

why are alkanes insoluble in water

A

water held by hydrogen bonds stronger than VDW forces in alkanes
but alkanes do mix w/ other non-polar liquids

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8
Q

what does cracking involve

A

breaking C-C bonds in alkanes

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9
Q

petrol is?

A

mixture of mainly alkanes w/ 4-12 carbons

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10
Q

alkenes are?

A

used as chemical feedstock, and are converted to polymers, pains, drugs

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11
Q

thermal cracking

A
  • high pressure (up to 7000kPa)
  • high temp (700-1200°K)
  • produces high % of alkenes
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12
Q

catalytic cracking

A
  • high temp
  • slight pressure (just more than atmospheric pressure)
  • zeolite catalyst
  • used mainly to produce motor fuels + aromatic hydrocarbons
  • zeolite: silicone dioxide and aluminium oxide
  • products are mostly branched alkanes cycloalkanes, aromatic compounds
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13
Q

internal combustion in an engine

A

produces large no. of pollutants, including NOx, CO, carbon and unburnt hydrocarbons

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14
Q

complete combustion

A

alkane+oxygen -> carbon dioxide+water
gives out heat; exothermic
store lots of energy in small weight
burns w/ a blue flame

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15
Q

incomplete combustion

A

alkane+oxygen -> carbon monoxide+water
carbon monoxide or carbon (soot) produced in limited oxygen supply
often happens w/ long chained hydrocarbons- need more O2 than short chain
burns w/ dirty yellow flame

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16
Q

what are catalytic converters

A

remove gaseous pollutants from internal combustion engines

17
Q

how do catalytic converters work

A

use precious metals to spread over mesh; honeycomb structure to increase s.a. so less expensive metal is needed. used as catalysts i think?

18
Q

what do catalytic converters do

A

reduce output of CO, NOx, unburnt hydrocarbons, forms N2, CO2, H2O

19
Q

CO2

A

greenhouse gas, climate change

20
Q

CO

A

incomplete combustion, poisonous

21
Q

NOx

A

enough energy for N2 and O2 in air to combine, may react w/ water vapour and O2 in air to form nitric acid; acid rain and photochemical smog

22
Q

sulfur dioxide

A

acid rain, produced when there are sulfur containing impurities in hydrocarbons.

23
Q

carbon particulates

A

asthma + cause cancer

24
Q

unburnt hydrocarbons

A

enter atmosphere, greenhouse effect, photochemical smog, health problems

25
Q

water vapour

A

relatively constant, but rising temps = more water vapour which increases temp further. however, clouds also reflect solar radiation so 🤷🏽‍♀️

26
Q

flue gas desulfurisation

A

sulfur dioxide can be removed from flue gases using calcium oxide or calcium carbonate

27
Q

acid rain formula

A

1SO2+2O2+2H2O->2H2SO4

28
Q

one method of flue gas desulfurisation

A

slurry of calcium oxide and water is sprayed into flue gas.

CaO+2H2O+SO2+1/2O2->CaSO4•2H2O

29
Q

another method of flue gas desulfurisation

A

CaCO3+1/2O2+SO2->CaSO4+CO2

30
Q

chlorination?

A

alkanes react w/ halogens under UV light to produce halogenoalkanes. UV breaks down halogen bonds, producing highly reactive free radicals

31
Q

initiation

A

breaking Cl2 bonds- 2 chlorine free radicals. energy from UV> energy holding Cl2 together. both atoms same; bond breaks homolytically- one electron each. C-H bond > UV, so doesn’t break

32
Q

initiation reaction

A

Cl+CL-> 2Cl•

33
Q

propagation stage 1

A

Cl• takes H atom from methane, forms hydrogen chloride (stable compounds), leaved methyl free radical

34
Q

propagation stage 1 reaction

A

Cl• + CH4 -> HCl + •CH3

35
Q

propagation stage 2

A

•CH3= very reactive. reacts w/ chlorine, forms Cl• and chloromethane (stable)

36
Q

propagation stage 2 reaction

A

•CH3 + Cl2 -> CH3Cl + Cl•

37
Q

propagation

A
  • chain part of the chain reaction
  • may take place 1000s of times before termination
  • conditions of reaction can be altered to favour termination step
38
Q

termination

A

two free radicals join, end chain reaction, form stable products, free radicals removed

39
Q

termination reactions

A

Cl• + Cl• -> Cl2
•CH3 + •CH3 -> C2H6
Cl• + •CH3 -> CH3Cl

Chemistry old (7 decks)

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