Alkanes Flashcards
General formula
CnH2n+2
Is there a double bond?
No
Fractional distillation process
- preheated oil passes into fractionating column
- temperature decreases upwards
- lower boiling point molecules condense higher up the column
Why do smaller alkanes have lower boiling points
As they have fewer and weaker LDF between molecules
What condenses higher and lower in the column
Petrol and gasoline condense higher up
Diesel and bitumen condense lower down
Cracking
- process
- what it does
Done by passing long hydrocarbon through a heated catalyst (Zeolite)
Large molecules break up into smaller ones
Reforming
What it does
How
Benefits
Used to convert straight-chain alkanes into branched-chain alkanes and cyclical hydrocarbons
Helps fuels burn smoother
Heat them with a catalyst (usually platinum)
Complete combustion equation
Alkane + oxygen —> carbon dioxide + water
Problems pollutants made by incomplete combustion cause
- Solid Carbon
Smoke or soot can be harmful when inhaled
Global dimming
Problems pollutants made by incomplete combustion cause
- carbon monoxide
Toxic gas causes death by binding with the iron in haemoglobin rather than oxygen
Problems pollutants made by incomplete combustion cause
- unburnt hydrocarbons
A small proportion released causing global warming
Problems pollutants made by incomplete combustion cause
- oxides of sulfur
Acidic oxide when dissolved in water
Can form sulphuric acid leading to acid rain which damages forests, lakes and limestone buildings
Problems pollutants made by incomplete combustion cause
- oxides of nitrogen
Produced by high temperatures in the engine
When dissolved in water it can produce nitric acid leading to acid rain
Catalytic converters
Platinum
3-way catalysts removed CO, unturned hydrocarbon and oxides of nitrogen
2NO + 2CO —> N2 + 2CO2
Alternative fuels
Biodiesel
Vegetable oils obtained from rapeseed and sunflowers
Alternative fuels
Bio alcohol
Bio ethanol
Ethanol is produced by the fermentation of sugars and then separated from large amounts of water
Positives and negatives of biofuels
Positives:
No exploration or drilling costs
Much closer to being carbon neural
Negatives:
Lots of land needed
Low yield
Substations costs in growing
Processing and transport
Positives and negatives of natural gas
Positives:
No land needed
Very high yield
Processing and transport costs are low
Negatives:
Exploration and drilling costs are high
Not carbon neutral
Radical definiton
A species that contains an unpaired electron
Substitution reactions of alkanes
Named example and condition
Halogenation (chlorination)
Occurs when the mixture is exposed to UV light
Name the 3 stages of halogenation substitution reaction of alkanes
- Initiation
- Propagation
- Termination
Describe initiation reaction
For chlorine and methane
UV radiation breaks the chlorine molecule into 2 chlorine atoms
Each chlorine atom takes one electron from the shared pair - homolytic fission
They are both radicals
Describe propagation reactions for methane and chlorine
Chlorine radicals are very reactive so remove a hydrogen atom from the methane molecule
Methyl radical is formed which is very reactive
It reacts with other chlorine molecules
What are propagation reactions
Where radicals and molecules collide to produce radicals and molecules
Describe termination reactions for chlorine and methane
Combination of reactions occur
A radical and a radical collide to form a molecule
Initiation equation for chlorine and methane
Cl2 —> Cl* + Cl*
2x propagation reaction equations for methane and chlorine
Cl* + CH4 —> HCl + CH3*
CH3* + Cl2 —> CH3Cl + Cl*
3x termination equations for methane and chlorine
Cl* + Cl* —> Cl2
Cl* + CH3* —> CH3Cl
CH3* + CH3* —> C2H6
