3.3.2.3 Combustion of Alkanes Flashcards
Why is the the combustion of alkanes important?
Alkanes are used as fuels
What is the complete combustion of an alkane?
When an alkane is burnt with oxygen in excess
So that the product is carbon dioxide and water
What is the incomplete combustion of an alkane?
The alkane doesn’t burn in an oxygen supply plentiful enough so the products formed are (along with water)
Carbon monoxide
Or
Soot
Is combustion exo or endo thermic?
Exothermic
What are soot and carbon monoxide considered to be?
Pollutants
What is the chemical formula of Carbon Monoxide and what is it’s state symbol?
CO (g)
What makes CO(g) dangerous?
It is a colourless, odourless toxic gas making it hard to detect
It binds irreversibly to haemoglobin
Results in suffocation
How is soot dangerous to people’s health?
Passes deep into lungs and cannot be removed
Why is soot bad for engine parts?
Reduces power of engine
Less energy given out by fuel
More fuel needs to be burnt to output same amount of energy
Why is soot bad for the environment?
Contributes to global dimming
What are greenhouse gases?
Gases in the atmosphere which can absorb and emit infra red radiation thus warming the atmosphere. They are not inherently bad and they are why the earth has a temperature which can sustain life
Give 5 examples of greenhouse gases
- Carbon dioxide
- Hydrocarbons
- Water vapour
- Methane
- Nitrous oxide (N2O)
Name 3 other main pollutants
- Unburnt hydrocarbons
- Sulphur dioxide
- Nitrogen oxides
How do unburnt hydrocarbons end up in the atmosphere?
Pass through engines unburnt
Why are unburnt hydrocarbons bad?
They waste fuel
They’re air pollutants
They’re carcinogenic
They’re greenhouse gases
How is the formation of unburnt hydrocarbons prevented?
Careful mixing of air with fuel reduces unburnt hydrocarbons
Can be removed in catalytic converters
How does the pollutant sulphur dioxide arise?
Fuels that contain sulphur undergo combustion
Write the equation for the combustion of sulphur
S + O2 => SO2
Why is sulphur dioxide bad for the environment?
As an acidic dioxide, it reacts with water to form acid rain. This damages limestone buildings and kills marine life
Why is sulphur dioxide harmful to health?
Causes respiratory problems
How is the formation of sulphur dioxide prevented?
Removed from fuel before burning
Or SO2 removed from fumed post combustion
What is the name of the mechanical process that removes
SO2 from fumes?
Flue gas desulphurisation
Describe the process of flue has desulphurisation
- Waste gases pass through scrubber, I.e. calcium oxide/calcium carbonate
- An acid-base reaction takes place
- Product of gypsum, CaSO3 which is used to make plasterboard
What causes the formation of nitrogen oxides?
Sparks and very high temperatures in engines cause N2 to react with O2 forming either NO or NO2, collectively referred to as NOx
