6.2 Alkanes Flashcards
Describing, fuels, pollution, reducing pollution, free radicals
What is homolytic fission?
It happens when each bonding atom receives one electron from the bonded pair forming two radicals
What is heterolytic fission?
When one bonding atom receives both electrons from the bonded pair
What are radicals?
Highly reactive, neutral species
How is a covalent bond formed from two radicals?
The radicals collide and the electrons are involved the bond formation
Describe the process of fractional distillation of crude oil
- The oil is pre-heated then passed into a column.
- The fractions condense at different heights and the temperature of column decreases upwards
- The separation of the fuels depends on boiling point which depends on size of molecules. The larger the molecule the larger the London forces
- Similar molecules (size, bp, mass) condense together and so are collected at the same fraction
- Small molecules condense at the top at lower temperatures and big molecules condense at the bottom at higher temperatures.
What is the reforming of crude oil?
It is processing of straight-chain hydrocarbons into branched-chain alkanes and cyclic hydrocarbons for efficient combustion.
Describe the 𝜎 (sigma) bond in alkane
The sigma bond is a covalent bond which has a direct overlap of the s orbitals of the bonding atoms.
What reactions will alkanes undergo?
Combustion and reaction with halogens
What type of reaction is combustion?
Oxidation reaction
What is the colour of the bunsen burner flame during complete combustion?
Blue flame
Which type of hydrocarbon are most likely to undergo incomplete combustion?
Longer chains
What are the pollutants formed in the combustion of alkanes?
Carbon monoxide, oxides of nitrogen and sulfur, carbon particulates and unburned hydrocarbons
What is the environmental impact of carbon monoxide?
It is toxic/poisonous, binds to haemoglobin
What is the environmental impact of soot (carbon)?
Asthma, cancer, global dimming
What are the environmental impacts of nitrogen oxides?
NO is toxic and can form smog
NO 2 is toxic and acidic and forms acid rain
Can react with VOCs to make PAN, which is found in photochemical smog.
What are the environmental impacts of unbranched hydrocarbons?
They contribute towards formation of smog
What is the importance of catalytic converter?
These remove CO, oxides of nitrogen and
unburned hydrocarbons (e.g. octane,
C8H18) from the exhaust gases, turning
them into less toxic products CO 2 , N 2
and H 2 O.
What are biofuels?
They are fuels developed from renewable resources.
What are the advantages of biofuels?
- Reduces of use of non-renewable fossil fuels
- Use of biodiesel is more carbon-neutral
- Fossil fuels can be used feedstock for organic compounds
- Less large scale pollution
What are the disadvantages of biofuels?
- Less food crops may be grown because crops for biofuel would be grown instead
- Reduction of rain forests have to be cut down to provide land
- Shortage of fertile soils
How are halogenoalkanes formed from alkanes?
Radical substitution
In the presence of what does alkane react with halogens?
UV light
What are the three stages of free radical substitution?
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
What compounds can be classified as aliphatic?
Alkanes, alkenes and alkynes.
What is the mnemonic for naming the first 4 alkanes?
Monkey Eats Peanut Butter
M-eth
E-th
P-rop
B-ut
How can alkanes be formed from crude oil?
Fractional distillation and cracking.
What are the products of fractional distillation?
Bitumen, fuel oil, diesel, kerosene, gasoline and refinery gases.
What is bitumen used for?
Roads and roofs.
What is fuel oil used for?
Fuel for ships and power stations.
What is diesel used for?
Fuel for vehicles.
What is kerosene used for?
Fuel for aircrafts.
What is gasoline used for?
Fuel for cars.
What are refinery gases used for?
Bottled gas.
What types of alkanes are more in demand?
Smaller chain alkanes.
What are the types of cracking?
- Thermal cracking: requires high temperature and high pressure. Makes alkanes and and lots of alkenes.
- Catalytic cracking: lower temperature and slight pressure with a catalyst like zeolite or aluminium oxide to make mainly aromatic compounds.
What is knocking?
When straight chain alkanes in a car engine explode rather than combust making combustion less efficient.
What does reforming use?
A platinum catalyst.
What do car exhaust fumes include?
Carbon monoxide, oxides of nitrogen, volatile organic compounds (VOCs).
What are catalytic converters?
Precious metals like platinum are coated on a honeycomb metal arrangement.
Why are catalytic converters in honeycomb arrangement?
A large surface area.
What is a renewable fuel?
A fuel that can be replaced over a short period.
What are the 3 main biofuels?
Biodiesel, bioethanol and biogas
What are the 3 limitations of free radical substitution?
Impurities, further substitution and substitution of different carbon atoms.
