Alkanes Flashcards
What are alkanes?
A homologous series of saturated hydrocarbons
What is a saturated hydrocarbon?
One which contains only single bonds between the carbon atoms
What is crude oil?
A mixture of different hydrocarbons
How can the different hydrocarbons in crude oil be separated?
Fractional distillation
Why can the different hydrocarbons in crude oil be separated by fractional distillation?
Because they have different boiling points
What happens during fractional distillation?
The mixture is vapourised and fed into the fractionating column, the vapours rise and condense at different levels, the fractions are collected
What is a fraction?
A group of compounds with similar boiling points that are removed at the same level of a fractionating column
What is cracking?
Breaking C-C bonds in alkanes to produce shorter chain alkanes and alkenes
Why is cracking used?
Longer chain molecules are less useful than shorter chain molecules but are more abundant
What are the conditions for thermal cracking
1200 K and 7000kPa
What are the main products of thermal cracking?
Alkanes and alkenes
What are the conditions for catalytic cracking?
720 K, atmospheric pressure and a zeolite catalyst
What are the main products of catalytic cracking?
Aromatic hydrocarbons and motor fuels
Why are alkanes commonly used as fuels?
They combust readily and release large amounts of heat energy
What is produced if alkanes undergo complete combustion?
Carbon dioxide and water
What is produced if alkanes undergo incomplete combustion?
Carbon monoxide or carbon particles and water
What pollutants are produced by internal combustion engines?
Oxides of nitrogen, carbon monoxide, carbon particles, sulfur dioxide and unburnt hydrocarbons
Why is carbon dioxide problematic?
It causes global warming
Why is carbon monoxide problematic?
It’s toxic
Why are carbon particles problematic?
They cause global dimming and breathing difficulties
Why are oxides of nitrogen problematic?
They cause acid rain
Why is sulfur dioxide problematic?
It causes acid rain
Why are unburnt hydrocarbons problematic?
They create smog
What pollutants released by internal combustion engines can be removed by a catalytic converter?
Carbon monoxide, oxides of nitrogen and unburnt hydrocarbons
What are the catalysts in catalytic converters?
Platinum and rhodium
What is the equation for the removal of nitrogen monoxide and carbon monoxide in a catalytic converter?
2NO(g) + 2CO(g) → 2CO2(g) + N2(g)
What causes oxides of nitrogen to be produced by internal combustion engines?
The oxidation of atmospheric nitrogen inside car engines
What causes sulfur dioxide to be produced by internal combustion engines
Burning fuels that contain sulfur impurities
How is sulfur dioxide removed from the atmosphere?
Flue gas desulfurisation
What happens during flue gas desulfurisation?
Flue gases are passed through a slurry containing calcium oxide and calcium carbonate which neutralise the sulfur dioxide to form calcium sulphite
Why are calcium oxide and calcium carbonate able to neutralise sulfur dioxide?
They are bases
What is the equation for the reaction between sulfur dioxide and calcium oxide?
CaO(s) + SO2(g) → CaSO3(s)
What is the equation for the reaction between sulfur dioxide and calcium carbonate?
CaCO3(s) + SO2(g) → CaSO3(s) + CO2(g)
What happens to the calcium sulphite produced by flue gas desulfurisation and why?
It is oxidised to calcium sulfate because it is more useful
When will alkanes react with halogens?
In the presence of UV light
What type of reaction is the reaction between an alkane and a halogen to form a halogenoalkane?
Free radical substitution
What is a free radical?
An atom or group with an unpaired electron
What are the 3 steps in a free radical substitution reaction?
Initiation, propagation, termination
What is the initiation step for the reaction between methane and chlorine in UV light?
Cl2 → Cl● + Cl●
What are the propagation steps for the reaction between methane and chlorine in UV light?
Cl● + CH4 → HCl + ●CH3
Cl● + CH4 → HCl + ●CH3
What are the termination steps for the reaction between methane and chlorine in UV light?
Cl● + Cl● → Cl2
Cl● + ●CH3 → CH3Cl
●CH3 + ●CH3 → C2H6
Why is the combination of 2 chlorine radicals not a proper termination step?
Because the UV light would break the chlorine molecule down again
What is a catalytic converter?
A device fitted in a car to reduce the amount of emissions from an internal combustion engine
What is fractional distillation?
A method of separating a mixture of substances according to their different boiling points
