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What is produced in combustion of alkane fuels?
Carbon monoxide, oxides of nitrogen and sulphur, carbon particulates, unburned hydrocarbons
What do catalytic converters do?
Improve air quality by removing pollutants before released from car exhaust
What is the structure of a catalytic convertor?
Honeycomb of ceramic material, coated with thin layer of metals e.g. rhodium, platinum or palladium
Large SA increases rate of reaction
How do catalytic converters work?
Carbon monoxide + unburned hydrocarbons + nitrogen oxides --> CO2 + H2O
In presence of catalyst
Examples of alternative fuels
Biofuels (bioethanol, biodiesel), nuclear, solar wind, wave
Why are biofuels a good alternative?
Crops take in CO2 for photosynthesis, so when burnt the CO2 is returned to the air, so overall they are carbon neutral
How is bioethanol produced?
Fermenting carbohydrates e.g. starch and sugar in crops like sugar cane
How is biodiesel produced?
Extracting and processing oils from crops e.g. rapeseed
Why is the production of sulphur and nitrous oxides harmful?
Forms acid rain
Sulphur reacts with oxygen in air to form SO2, SO2 reacts with water in clouds to form H2SO4
What are the conditions for cracking?
Catalyst: silica or alumina
Why are silica and alumina good catalysts for cracking?
- 3D structure in which silicon, aluminium and oxygen atoms form tunnels and cavities into which small molecules can fit
- Can be developed with active sites to favour the shapes and sizes of molecules which react to give desired products
Converting long chain alkanes (12+ carbons) into shorter chain hydrocarbons (alkanes, cycloalkanes, alkenes, branched alkenes)
Processing straight chain hydrocarbons into branched chain alkanes and cyclic hydrocarbons
What are the conditions for reforming?
Catalyst: platinum or rhodium
What is a radical?
A species with an unpaired electron, formed by homolytic fission of a covalent bond
What are the main reasons for pollution caused by petrol/diesel fuels?
- Engines do not burn fuel completely
- Fuel contains impurities
- High temperature causes nitrogen and oxygen in air to react
Why do cars produce oxides of nitrogen?
- Engine temp can rise to 2800*C
- Nitrogen reacts with oxygen to form nitrogen monoxide
- NO reacts with more O2 to form NO2
- NOx reacts with water + O2 to form nitric acid
- Nitric acid leads to acid rain
Why do cars produce oxides of sulphur/lead to sulphuric acid production?
- Sulphur impurities in alkane reacts with hydrogen to form hydrogen sulfide
- H2S reacts with O2 to form SO2, then sulphur
- Sulphur is used to form sulphuric acid
- H2SO4 leads to acid rain
What is the reaction of alkanes with oxygen called?
What is produced in complete combustion?
Carbon dioxide and water
Why does incomplete combustion occur?
If O2 is in short supply
What is produced in incomplete combustion?
Soot (carbon) and carbon monoxide
What type of reaction is the reaction of alkanes with Cl or Br?
What is required for halogenation to occur?
UV light, causes homolytic fission of Cl/Br to form free radicals
What are the three steps of free-radical substitution?
Initiation, propagation, termination
Why is the free-radical substitution method limited?
Propagation can continue, so further substitution can occur to form other molecules, not just the desired product of a chloroalkane
Recommended textbook explanations
Sarquis, J., Sarquis, M.
Interactive Science: Physical Science
Introductory Chemistry: A Foundation
Donald J. DeCoste, Steven S. Zumdahl
Foundations of Physical Science (Florida Edition)
Tom C. Hsu
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