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Chemistry (AS) > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

What is an alkane?
What’s its General Formula?

A

A saturated hydrocarbon.
C(n) H(2n+2)

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2
Q

Explain a hydrocarbons solubility in water

A

Not soluble in water
C and H have similar electronegativities within the c-h bonds and symmetrical structure which results in a non polar molecule
Non polar molecules are not soluble in a polar solvent like water

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3
Q

Which Intermolecular forces do alkanes have?

A

VDW only
(Not polar so no permanent dipole & doesnt form H-O, H-F, H-N so no Hydrogen bonding either)

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4
Q

What reactions will alkanes undergo?

A

Combustion and Reactions with Halogens

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5
Q

What is Crude Oil?

A

a Mixture of saturated hydrocarbon chains lengths each with similar boiling points and properties

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6
Q

Name all of the Crude oil fractions from Highest to lowest Boiling point (8)

A

Gases - Cooking gas - 20
Petrol- Automotive Fuel - 70
Naphtha - Chemicals -120
Kerosene - Jet fuel- 180
Diesel - Trucks - 260
Lubricating Oil- oils for cars and machines - 300
Fuel oil- Tanker Ships - 350
Bitumen Residue - Tarmac

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7
Q

How does Fractional Distillation Work (4 points)

A

Crude oil is heated until mostly vapour

Vapours pass into fractionating column and tower

vapours rise through trays and bubble caps

Vapours of lower boiling point due to smaller hydrocarbon chains raise higher so condense in higher trays of temperature closest to its boiling point

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8
Q

What is Fracking
What are the pros/cons

A

1)Natural gas held in shale rock

Drill into shale, forced pressurised water and sand until fractures occur and collect said gas

2)pro- reduces foreign import of gas and electricity for home heating

Con - Can cause seismic disturbances, can cause chemically contaminated water

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9
Q

What is cracking

A

Conversion of a long chain alkane to Shorter chain alkane with the byproduct of an alkene
By breaking a c-c bond

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10
Q

What are the conditions of thermal cracking?

A

700-1200K
7000 kPa of pressure
Process can only be operated for very short windows of time to prevent carbon and hydrogen decomposition.

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11
Q

What are the Products of thermal cracking

A

. High number of alkenes
. Unselective of desired chain length (c-c bond can break at any point —> high number of shorter carbon chains
.can also produce H2

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12
Q

What are the conditions for Catalytic Cracking?

A

720K
Slightly higher pressure then an atmosphere
Zeolite Catalyst ( SiO2 & Al3O3) in a honeycomb structure to give a large surface area

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13
Q

What are the Products of Catalytic Cracking?

A

Mixture of:
Branched Alkanes
Cyclo Alkanes
Aromatic Compounds
Mostly Gaseous Chain lengths ( < 5)

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14
Q

What is Incomplete combustion and what are the common products of it?

A

Combustion reactions in a limited supply of oxygen

CO- Carbon Monoxide - Poisonous
C-Carbon-particulates-soot - asthma cancer and global dimming

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15
Q

What hydrocarbon chains are likely to incompletely combust?

A

Longer Chains

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16
Q

How are Nitrogen oxides typically formed?
What is the environmental impacts of nitrogen oxides?

A

Produced from engines at high temperatures which acts as a catalyst to bind nitrogen and oxygen
Forms nitric acid —> acid rain
and photochemical smog

17
Q

What is the environmental impact of sulphur dioxides

A

Forms sulphuric acid in the atmosphere—-> acid rain

18
Q

What is the environmental impact of carbon dioxide

A

Greenhouse gas —> Global warming
Increases global temperatures by reflecting space bound photons back at the earths surface heating the earth up and speeding up climate change

19
Q

What’s the Environmental impact of water vapour

A

Greenhouse gas —> Global warming
Increases global temperatures by reflecting space bound photons back at the earths surface heating the earth up and speeding up climate change

20
Q

How do you desulphur gasses from power stations

A

Addition of Calcium oxide will neutralise the sodium dioxide to make it less acidic and therefore cannot polute the atmosphere

21
Q

How are halogenoalkanes formed from alkanes

A

Free radical Substitution
X2 + Uv Light

22
Q

State and explain the 3 stages of free radical substitution

A

Initiation - Breaking halogen bond to from free radicals

Propagation - Reaction where products are formed but free radicals remain

Termination - Free radicals removed and stable products formed

23
Q

What is the condition for Free radical substitution

A

UV light

24
Q
A
25
Q

What is the ozone’s layers function?

A

Protects the earth from harmful exposure of too many uv rays

26
Q

How do CFCs break down the ozone layers

A

Free Radial Substitution
Decomposes Ozone into oxygen

27
Q
A

Chlorine free radicals act as catalysts in other reactions of the decomposition of ozone

Chemistry (AS) (16 decks)

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