3.3.2.3 Combustion of alkanes Flashcards
Which alkanes undergo incomplete combustion when burnt?
Alkanes in a short supply of oxygen
Longer chain hydrocarbons as they need more oxygen to burn
Cyclohexanes - due to C:H ratio
Which alkanes form undergo complete combustion when burnt?
Shorter chain alkanes
E.g. methane, paraffin, propane
What are the harmful products when hydrocarbon-based fuels burn?
Carbon monoxide - CO Nitrogen oxides - NO, NO2, N2O4 Sulfur dioxide - produced from sulfur impurities Carbon particulates - soot Unburnt hydrocarbons - greenhouse gases Carbon dioxide - greenhouse gas Water vapour - greenhouse gas
What is flue gas desulfurisation?
Coal or natural gas contains sulfur compounds
When these are burnt, sulfur dioxide is released which combines with oxygen and water in the atmosphere to form sulfuric acid
Gases given out by a power station is called flue gas
Removing sulfur from this = flue gas desulfurisation
What are some methods of flue gas desulfurisation?
Adding calcium oxide and water
This reacts with calcium oxide and water to form calcium sulfite
This can be further oxidised to calcium sulfate (CaSO4.2H2O)
What are catalytic converters?
A honeycomb made of a ceramic material coated with platinum and rhodium metals (catalysts)
Honeycomb provides a large surface area
As polluting gases (carbon monoxide, nitrogen oxides, unburnt hydrocarbons) pass over the catalyst, they react with each other to form less harmful products
Why is carbon monoxide a pollutant?
A toxic gas that prevents oxygen from being transported by red blood cells
Why are sulfur dioxide and nitrous oxides pollutants?
Acidic gases that cause air pollution and acid rain
Both are associated with respiratory problems
NO is recognised as an asthma trigger
Why are carbon particulates pollutants?
It can damage lung tissue and cause increased reflection of sunlight which causes global dimming
Why are unburnt alkanes and nitogen oxides pollutants?
They react in the presence of sunlight to produce a mixture of secondary pollutants known as photochemical smog. One secondary pollutant is ozone which damages the lungs and eyes
What reactions are caused by catalytic converters?
2CO + 2NO = N2 + 2CO3
Catalyses the oxidation of unburned hydrocarbons to CO2 and H2O
