3.3.2.3. Combustion of Alkanes Flashcards
Why are alkanes used as fuel?
When they are burned down, they release energy via combustion reaction (exothermic)
What are the 2 types of combustion?
Complete and incomplete
When does complete combustion happen?
When there is an excess of oxygen
What are the products of complete combustion?
CO2 and H2O
When does incomplete combustion happen?
When there is a limited amount of oxygen
What are the products of incomplete combustion?
CO or C and H2O
Why is carbon monoxide known as a silent killer?
It is odourless, tasteless and colourless.
- For safety, have regular maintenance checks or get a CO alarm
How does the internal combustion engine work?
Small amount of fuel and lots of oxygen is drawn into the combustion chamber.
The fuel is ignited with an extremely high temperature (a spark)
The fuel the burns explosively, which forces the movement of engine parts.
Products exit via exhaust.
What causes side reactions in the combustion engine?
Pressure and extreme temperatures
What are some side products produced in the combustion engine?
Nitrogen: oxides of nitrogen (air is drawn into the chamber, which is 78% nitrogen). Can get nitrogen monoxide (NO) or nitrogen dioxide (NO2).
Sulphur: From impurities in crude oil which end up in fuels. Usually SO2.
Describe the greenhouse effect
- Short wavelength radiation from the Sun enters the Earth’s atmosphere.
- Objects/ materials absorb this and re-emit it as longer wavelength radiation
- Greenhouse gasses trap and absorb this longer wavelength radiation, causing these molecules to vibrate more and increase the temperature of the Earth
* only molecules with polar bonds can be greenhouse gasses
Describe global warming
Mainly due to ‘enhanced greenhouse effect’ and increasing CO2 levels, so more long wavelength radiation is absorbed and trapped leading to higher temperatures in the atmosphere
What contributes to acid rain?
Nitrogen Oxides (NOX)
How is acid rain formed?
SO2 reacts with acid rain in the air to produce sulphurous acid (H2SO3), which can further be oxidised in the presence of oxygen in the air to become H2SO4.
What are the impacts of acid rain?
Destroys trees and vegetation
Corrodes limestone and buildings and statues
Kills fish in lakes
What causes photochemical smog?
Pungent and toxic gasses and solid particles suspended in the air close to the surface of the Earth
What forms photochemical smog?
NOX, SO2, Soot and unburnt hydrocarbons reacting with sunlight
What are the health impacts of photochemical smog?
Irritated eyes
Severe lung disease
How can we remove pollutants?
Catalytic converters
Removal of suphur
What do catalytic converters remove?
Carbon monoxide
Nitrogen oxides
Unburnt hydrocarbons
- that are released from the internal combustion engine
What is the goal of a catalytic converter?
By converting toxic gasses into less toxic gasses, can remove CO, NOx and unburnt hydrocarbons like octane
What is the structure of catalytic converters and how do they work?
Honeycomb structure made of a ceramic material and covered in a thin layer of platinum/rhodium/palladium catalysts
Why is a honeycomb structure used in a catalytic converter?
Increased surface area so faster rate of reaction
Why is a thin layer of catalyst used in a catalytic converter?
Less metal needed, so cheaper
What are the reactions that happen in a catalytic converter?
2NO+2CO -> N2+2CO2
C10H22 +31NO -> 10CO2 +11H2O +31/2 N2
When are sulphur impurities in fuels removed?
Prior to being fuelled in cars
- but is not economically viable for fuel used in power stations, so instead it is removed through flue gas desulphurisation
How does flue gas desulphurisation work?
Gasses are passed through a slurry of calcium oxide and calcium carbonate (CaO and CaCO3).
These are both bases, so neutralise the SO2 to form CaSO3, which is then oxidised to form CaSO4 used in construction
What are the equations for flue gas desulphurisation?
CaO + SO2 -> CaSO3 (calcium sulphite)
CaCO2 +SO2 -> CaSO2 + CO2
CaSO3 + [O] -> CaSO4
What type of environmental problem do nitrogen oxides cause?
Can form NO2, which can form acid rain
What type of environmental problem can carbon monoxide cause?
Toxic - death
What type of environmental problem can unburnt hydrocarbons cause?
Photochemical smog
What type of environmental problem can soot cause?
Global dimming
Why does carbon dioxide cause global warming?
Double bonds can absorb infrared radiation, which causes the molecule to vibrate, so IR transferred to other molecules
