Combustion of Alkanes
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Why are alkanes generally unreactive?
Alkanes have strong C-C and C-H bonds and are non - polar, making them unreactive towards acids, bases, oxidising agents and reducing agents
What are the products of complete combustion?
Carbon dioxide (CO2) and water (H20)
When does incomplete combustion occur, the circumstances?
Incomplete combustion occurs when there is a limited supply of oxygen
What poisonous gas is produced during incomplete combustion?
Carbon monoxide is produced which binds to haemoglobin, reducing oxygen transport in the blood
Why is carbon monoxide (CO) harmful?
CO is harmful because it binds to haemoglobin, reducing oxygen transport in the blood
How does the number of carbon atoms in an alkane affect the energy released during combustion?
The more carbon atoms present in an alkane, the greater the energy released during combustion, due to more bonds being broken and formed
What happens when oxygen is extremely limited in combustion?
Carbon (soot) is formed instead of carbon monoxide or carbon dioxide
What are the 7 main polluting products produced when hydrocarbon - based fuels burn?
Carbon monoxide (CO) Nitrogen oxides (NOx) Sulfur dioxide (SO2) Carbon particulates Unburnt hydrocarbons Carbon dioxide (CO2) Water vapour
How are nitrogen oxides (NOx) formed in a petrol engine?
At high temperatures, nitrogen and oxygen from the air react: N₂ (g) + O₂ (g) → 2NO (g)
What environmental problems do nitrogen oxides cause?
They form nitric acid when reacting with water and oxygen, contributing to acid rain and photochemical smog
What environmental problems does sulfur dioxide cause?
They react with oxygen and water to form sulphuric acid, contributing to acid rain
How do sulfur and nitrogen oxides make rain more acidic?
They dissolve in rainwater, forming stronger acids like sulfuric acid and nitric acid
What environmental impacts does acid rain have?
It damages trees, harming aquatic life and corrode buildings
What are carbon particulates and what problems do they cause?
Solid carbon particles - they exacerbate asthma, cause cancer and contribute to global dimming
Why are unburnt hydrocarbons harmful?
They are greenhouse gases and contribute to photochemical smog, causing health problems
What are flue gases?
Gases released from power stations during the combustion of fossil fuels
What is flue gas desulfurisation?
The process of removing sulfur dioxide from flue gases to reduce acid rain
What are the two main methods of removing SO₂ from flue gases?
• Calcium oxide (lime) slurry method • Wet scrubbing method using calcium carbonate (limestone)
What chemicals are used in the calcium oxide slurry method?
Calcium oxide mixed with water to form a slurry
What happens in the calcium oxide slurry method, and what is produced?
Calcium oxide and water are sprayed into the flue gas, which reacts to form calcium sulfite. It is further oxidised to form gypsum (calcium sulfate)
Give the overall reaction for flue gas desulfurisation using calcium oxide
CaO (s) + 2H₂O (l) + SO₂ (g) + ½O₂ (g) → CaSO₄·2H₂O (s)
What is the main substance used in wet scrubbing?
Calcium carbonate (CaCO₃) (limestone) dissolved in water
How does calcium carbonate (wet scrubbing) method remove sulfur dioxide? What product is formed when SO₂ reacts with CaCO₃ slurry?
The acidic SO₂ is neutralised by CaCO₃ Calcium sulfate (CaSO₄) precipitate
What is the wet scrubbing method for removing sulfur impurities from flue gases? • force - polluted gas - pool - CaCO3 + H2O • CaCO3 neutralises gas • Calcium sulfate formed
1) Forcing polluted gas through a pool of liquid containing calcium carbonate dissolved in water 2) The calcium carbonate neutralises the acidic gas and removes it 3) The sulfur dioxide then reacts with slurry to form calcium sulfate