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Chemistry - Organic > Organic 1 - Chapter 12: Alkanes > Flashcards

Organic 1 - Chapter 12: Alkanes Flashcards

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1
Q

What is an alkane?

A

Saturated hydrocarbon with only C-C and C-H bonds

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2
Q

What are alkanes used for and why?

A

Fuels, lubricants and feedstock due to being unreactive

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3
Q

What is the general formula for a chain alkane?

A

CnH2n+2

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4
Q

What is the general formula for a ring alkane?

A

CnH2n

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5
Q

Describe the physical properties of alkanes
Mention polarity, boiling point, solubility and reactivity

A

Polarity: Almost non-polar as electronegativity of carbon and hydrogen are similar

MP + BP: Bigger chain -> more Van der waals forces -> Higher MP+ BP

Solubility: Insoluble in water as hydrogen bonds in water are stronger than vdw forces between alkane molecules, can mix in other non-polar liquids

Reactivity: Relatively unreactive due to strong C-C and C-H bonds. They do burn and react with halogens under suitable conditions

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6
Q

Describe the steps for the fractional distillation of crude oil

A

Crude oil heated in furnace

Mixture of liquid + vapour pass into fractionating tower which is cooler at top than bottom

Vapours pass up tower via a series of trays containing bubble caps until they arrive at a tray where they can condense to liquid

The mixture of liquids that condense on each tray is piped off

Shorter chain hydrocarbons condense near top of tower as it is cooler

Thick residue collects at the base (bitumen) often processed to give more valuable products as supply > demand

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7
Q

What is broken during fractional distillation?

A

Vdw forces between the molecules break during vaporisation and reform on condensing

NOT COVALENT BONDS

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8
Q

What is fracking?

A

Natural gas is trapped within shale rock:

Drill into the shale

Force pressurised water with chemicals mixed with sand into the shale. Chemicals such as HCl and methanol added to break shale and prevent corrosion

Shale fractures -> trapped gas flows to surface

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9
Q

Why are people against fracking?

A

People do not like the infrastructure of wells and associated ‘traffic’ around them

Concern about the amount of water used

Concern about chemical additives polluting water supply

Fracking occasionally causes small earthquakes

Burning natural gas creates CO₂ which causes global warming

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10
Q

What are the benefits of cracking?

A

Shorter more useful chains produced

Some products are alkenes which are more reactive than alkanes

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11
Q

What are the conditions required for thermal cracking?

A

700-1200K
7000kPa

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12
Q

What are the main products of thermal cracking?

A

High proportion of alkenes

Alkanes and hydrogen can also be produced

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13
Q

Why are hydrocarbons not subjected to thermal cracking for long durations?

A

To avoid too much decomposition, ultimately to just carbon and hydrogen

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14
Q

How does thermal cracking work?

A

C-C bonds break

1 electron from the pair in the covalent bond goes to each carbon

This produces 2 shorter chains with a free radical at the end

They react to form shorter chain molecules

There is not enough hydrogen atoms to produce 2 alkanes, therefore one of the new chains must be an alkene

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15
Q

What are the conditions required for catalytic cracking?

A

720K
Just above atmospheric pressure
Zeolite catalyst

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16
Q

What are the main products of catalytic cracking?

A

Alkanes
Cycloalkanes
Aromatic compounds

These are then separated via fractional distillation

17
Q

What are the products of complete combustion?

A

Carbon dioxide

Water

18
Q

What are the products of incomplete combustion?

A

Water

[ Carbon monoxide
Soot (Carbon)
Products will depend on oxygen availability which you can calculate with a chemical equation ]

19
Q

What are some pollutants that may be produced from burning fuel derived from crude oil?

A

CO: Carbon monoxide
NOₓ: Nitrogen oxides
SO₂: Sulfur dioxide
CO₂: Carbon dioxide
H₂O: Water vapour
Carbon particulates
Unburnt hydrocarbons

20
Q

How is carbon monoxide produced from combustion of crude oil and why is it a pollutant?

A

Produced by incomplete combustion

It is poisonous

21
Q

How are nitrous oxides produced from combustion of crude oil and why is it a pollutant?

A

Produced when there is enough energy for nitrogen and oxygen in the air to combine

Happens in petrol engines due to high temperatures

Nitrous oxides cause photochemical smog

They can also react with water vapour and oxygen in the air to form nitric acid contributing to acid rain. However. nitric acid itself does not cause photochemical smog

22
Q

How is sulfur dioxide produced from combustion of crude oil and why is it a pollutant?

A

Sulfur-containing impurities present in crude oil. This combines with water vapour and oxygen in the air to form sulfuric acid
SO₂(g) + ½O₂(g) + H₂O(l) -> H₂SO₄(l)

This causes acid rain

23
Q

How is carbon dioxide produced from combustion of crude oil and why is it a pollutant?

A

Produced from the complete combustion of hydrocarbons

It is a greenhouse gas

24
Q

How is water vapour produced from combustion of crude oil and why is it a pollutant?

A

A product of combustion

It is a greenhouse gas

25
Q

How are carbon particulates produced from combustion of crude oil and why is it a pollutant?

A

A product of incomplete combustion

It can cause global dimming, cancer and exacerbate asthma

26
Q

How are unburnt hydrocarbons produced from combustion of crude oil and why is it a pollutant?

A

May be produced from incomplete combustion

It is a significant greenhouse gas and contributes to photochemical smog

27
Q

What methods are used for flue gas desulfurisation?

Needs better explaination

A

A slurry of calcium oxide (lime) and water is sprayed onto the flue gas to form calcium sulfate

Calcium carbonate can be used instead of calcium oxide which also forms CO₂

28
Q

What is a catalytic converter made of?

A

Honeycomb made of ceramic coated with platinum and rhodium, which are the catalysts

29
Q

What is the purpose of a catalytic converter’s honeycomb shape?

A

Large surface area. Reactions between pollutants can only happen on the surface of the catalyst

30
Q

Why does infrared radiation get trapped by greenhouse gases?

A

It has a longer wavelength than visible light, which passes through

31
Q

Why are CFCs a problem in the atmosphere?

A

C-Cl bond breaks homolytically (when it splits into 2 free radicals) in the presence of UV radiation and reacts with ozone. This causes a chain reaction that damages the ozone layer

Chemistry - Organic (5 decks)

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