3.3.2 Alkanes Flashcards
What are alkanes
Saturated hydrocarbons
Single covalent bonds
Only c and h
Name by longest section of the chain
Properties of alkanes
Polarity - non polar small difference in electronegativity between the hydrogen and the carbon
Bp - longer the chain the higher the bp. As more electrons so stronger van der waals
Solubility - non polar so don’t dissolve in water
Crude oil origins
Made form dead organic matter at the bottom of the ocean
Contains sulphur and sulphur oxides that when burnt creates acid rain
Fractional distillation process
Hot crude oil is passed in#
All is heated and moves up the colomb as vapour
The colomb gets colder as it goes up
Teh fractions condense at ditrenrt levels and are piped of in fractions
Fractional distillation order
Long - short
Bitumen,Fuel oil,gas oil,diesel, kerosine,naphtha,petrol, gasoline, gas
Cracking why ?
Fractional distillation contains a higher fraction oof long chinese than needed
So cracked into smaller ones
Thermal cracking
800-900 degrees
Up to 7000 kpa
Makes short alkanes and alkenes
Used for making polymers
Done with no air
Could lead to total decomposition
Catalytic cracking
500 degrees
Just above atmospheric pressure
Silica and aluminium oxide zeolite catalyst
Makes branched alkanes,alkenes,aromatics,cycloalkanes
Used for moto fule
Complete combustion
Lots of o2 needed
Makes co2 and h2o
Make sure that it is balanced
Incomplete combustion
The carbon only undergoes partial oxidation so formes co
Unburnt carbon released as soot
Makes a mixture of carbon, carbon monoxide and h20
Co binds with haemoglobin in cells and stops them from carrying oxygen
Environmental problems
When combustion takes place releases heat meaning high temperatures
Meaning the nitrogen and the oxygen in the air react
Foming nitrogen oxides eg nitrogen dioxide
As well as unburnt hydrocarbons
The unburnt hydrocarbons with light react with the the nitrogen oxides to produce photochemical smog
Acid rain
So2 reacts with o to form so3 wich creates acid rain Contains dissolved co2 from atmosphere
An be created by so2 to make sulfuric acid (most common)
Or react with no2to create nitric acid
Catalytic converters
Ceramic honeycomb coated in platinum or rhodium (Pt,Pd,Rh,Ir)
Harmful gases pass over and react to form less harmful
Flue - gas desulfurization
Slurry of calcium oxide and water sprayed into the flue gas which reacts
Calcium oxide + water → calcium sulfate
Further oxidation gets you gypsum (ssalable product)
You can use calcium carbonate instead of calcium oxide to neutralise the gas)
Free radical substitution ozone due to cfcs mechanisms
This is a chain reaction which means it causes depletion of the ozone
The ozone layer is in the stratosphere
cl. + o3 -> clo. + o2
clo. + o3 -> 2o2 + cl.
Free radical substitution mechanism example
initiation
propagation - making hcl step 1
termination
Free radical substitution steps
Initiation - uv provides the energy needed for homolytic fusion of the chorine (free radicals made)
Propagation (happens in 2 stages) - create a new different free radical and then recreate the first free radical
Termination - two free radicals join together and a variety of molecules are formed
Free radicals
Very reactive species
Formed when a covalent bond breaks and one electron goes to each atom - homolytic fusion
Important facts section
Nitrogen comes in a pair never nitrogen on there own
Think if fule is a solid
2CO + 2NO → CO2 +N2
What catalysts are used in the catalytic converters
Platinum palladium - carbon monoxide → carbon dioxide
Platinum rhodium - oxides of nitrogen → n2 + o2
What zeolite catalyst is used in catalytic cracking
Silicon dioxide, aluminium oxide
How is water a greenhouse gas
More clouds that reflect the solar radiation
How are haloalkanes formed
Halogen + alkane with UV to start the reaction
Chloro fluoro carbons facts
low bp,c-cl has the lowest bond empathy which is why it breaks of first, cheap and non toxic, found in pollutants,aresols
