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Organic Chemistry > 3.2 Alkanes > Flashcards

3.2 Alkanes Flashcards

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1
Q

What is an alkane

A

A saturated hydrocarbon containing C-H bonds only

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2
Q

General formula

A

CnH2n+2

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3
Q

Are their bonds polar and why/why not?

A

Non-polar

Carbon and hydrogen have similar electronegativities

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4
Q

Intermolecular forces?

A

Only Vander waals forces of attraction

Bonds are non polar

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5
Q

Solubility in water?

A

Insoluble because hydrogen bonds in water are stronger than alkanes’ vander waals forces of attraction

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6
Q

How reactive are alkanes

A

Very unreactive

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7
Q

Which reaction 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
THEREFORE NON-RENEWABLE

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9
Q

Name fractions from high to low

A 
Gases - fuel on site
Gasoline/ petrol/ naphtha- cars
Kerosine/ paraffin- jet fuel, lighting
Diesel oil- lorries/ taxis
Lubricating oil/ waxes - candles, engine oil 
Fuel oil - ships, power stations
Tar/ bitumen - roads, roofing
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10
Q

What is fractional distillation and how does it work?

A

Crude oils heated until mostly vaporised

Passed into fractionating tower that is cooler at the top than the bottom

Liquid fractions are piped off at the bottom
Vapours rise up the column and- via trays and bubble caps- condense when temperature is less than their boiling point

Shorted chain hydrocarbon 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 held within 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

Pros/ cons 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, chemicals 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 long chain alkane, which is nkt very economically valuable, into shorter chain alkanes (more economically valuable as can be used as a fuel) and an alkene ( more reactive, starting point for many products)

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14
Q

What are 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 main products of thermal cracking

A

Alkenes

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17
Q

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

18
Q

What are the main products of catalytic cracking?

A

Cycloalkanes, aromatic hydrocarbons, branched alkanes

19
Q

What is a fuel

A

Something which releases heat energy when combusted

20
Q

What type of hydrocarbons are most likely to go through incomplete combustion

A

Longer chains

21
Q

Environmental impact of carbon monoxide

A

Toxic and poisonus

22
Q

Environmental impact of nitrogen oxides?

A

Form nitric acid —-> acid rain,

Photochemical smog

23
Q

Environmental impact of sulfur impurities/ sulfur dioxide

A

Form sulfur of acid—> acid rain

24
Q

Environmental impact of soot (carbon)

A

Asthma , cancer, global dimming

25
Q

Environmental impact of co2

A

Green house gas—> global warming, increase global temp, speeds up climate change

26
Q

Environmental impact of water vapour

A

Green house gas—> global warming,

Global dimming

27
Q

What are flue gases

A

Gases given out by power stations

28
Q

Write 2 equations for two different ways to desulfurise flue gaseS

A

Ca(s) + 2H2O(l) +SO2 +1/2O2(g) —> CaSO4 . 2H2O (s)

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

29
Q

What are catalytic converters made up of

A

Ceramic honey comb coated with platinum, palladium and rhodium (pt, Pd and Rh) metals

30
Q

What do they catalyse (equations)

A

They catalyse these reactions of products from car exhausts :

2CO(g) + 2NO—> N2(g) +2CO2(g)

Hydrocarbons + NO —> N2 +CO2 +H2O

31
Q

What are green house gases

A

Gase which trap Infared radiation, making the earth act like a greenhouse

32
Q

What is the green house effect and how does it contribute to global warming?

A

Greenhouse gases trap infrared radiation in the atmosphere, atmosphere heats up —> global warming

33
Q

Define carbon neutral activities

A

Activities that produce no net/ overall carbon dioxide emissions

34
Q

How are halogenoalkanes formed from alkanes

A

Free radical substitution reaction

35
Q

What are the three stages of free radicals substitution

A

Initiation- breaking halogen bond to form free radicals

Propagation - chain part of the reaction where products are formed but free radical remains

Termination- free radicals removed, stable products formed

36
Q

What are the conditions needed for the formation of free radical chlorine atom

A

Presence of UV light

37
Q

Write equations for the reaction of CH4 with Cl2 to form CH3Cl

A

Initiation: Cl2 —> 2Cl. ( in presence of UV light)

Propagation: Cl. +CH4 —> HCl +.CH3
.CH3 + Cl2 —> CH3Cl + Cl.

Termination:
.CH3 + .Cl —> CH3Cl
.Cl + .Cl —> Cl2
.CH3 + .CH3 —> CH3CH3

38
Q

What is the ozone’s function

A

Protects the earth from harmful exposure to too many uv rays

39
Q

How do CFC’s break the ozone down

A

Free radical substitution

40
Q

Write the equation for the overall decomposition of ozone into oxygen

A

2O3 —> 3O2

41
Q

Write free radical substitution equations to show how Cl free radicals catalyse and break down O3

A

Cl2 —-> 2Cl.
Cl. + O3 —> ClO. +O2
ClO. + O3 —> 2O2 + Cl.

Overall : 2O3 —> 3O2

42
Q

name fractions from high to low

A 
gases- fuel on site 
gasoline/ fuel/ naphtha - cars
kerosene/ paraffin - jet fuel, lighting
diesel oil- lorries taxis
lubricating oil waxes - candles, engine oil
fuel oil- ships power stations 
tar/ bitumen- roads , roofing

Organic Chemistry (2 decks)

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