3.2 Alkanes Flashcards
What is Fractional Distillation?
The process of separating crude oil into groups of hydrocarbon with a similar number of carbons
What are the three stages of fractional distillation?
Evaporation ,Condensation, Collection
What are the features of evaporation in fractional distillation?
Crude oil is heated until it evaporates
Crude oil vapour is put into a fractionating column
What are the features of condensation in fractional distillation?
Temperature is higher at the bottom of the column
Long chains condense at bottom
Short chains are gasses and collect at the top
What are Alkanes?
Saturated Hydrocarbons that can form cycloalkanes and functional group isomers
What temperature is crude oil vaporised at?
350 °c
How are alkane products used?
- Gasses- Can be used in gas stoves
- Kerosene- Used in jet fuel
- Bitumen- Used in roofing and tarmac
What is the polarity of alkanes?
Almost non-polar (en of H + C are similar)
Only IMF are van der Waals
What is the pattern with the boiling points of Alkanes?
Boiling point increases as chain length increases due to more vdW
5> carbons= gasses at room temp
5< x <18 carbons = liquid at room temp
18< = Solids (waxy feel)
What is the solubility of Alkanes?
- Insoluble in water as water molecules are held to get her by H bonds
- Will mix with other non polar molecules
What are the reactivity of alkanes?
Largely uncreative due to strong c-c and c-h
Will only react with halogens,under certain conditions
Will burn
(Lots of O2 = CO2 + H2O)
(Restricted supply of O2= CO / C
What is cracking?
Breaking longer chain fractions into shorter ones
What does cracking result in?
Shorter more useful chains (e.g petrol)
Some products are Alkanes which are more reactive
Why are harsh conditions necessary for catalytic cracking?
Alkanes are mostly unreactive
What are the conditions for thermal cracking?
High temp (700K - 1200K)
High pressure (up to 7000 Kpa)
What happens in thermal cracking?
C-C bonds so one electron goes to each carbon atom
Initially two shorter chains are made ending with a C free radical
There isn’t enough hydrogen to make two Alkanes so one has a double bond and forms and alkene
What is catalytic cracking?
Using a catalyst to crack alkanes resulting in lower temperatures and pressure
What are the conditions catalytic cracking occur in?
720 K temperature
Just over 1 atm
What is the catalyst called in catalytic cracking and what are the features?
- Uses a zeollic catalyst consisting of silicon dioxide + aluminium oxide
- Large Surface area
- Honeycomb structure
- Acidic
When is catalytic cracking predominantly used?
To produce motor fuels
Or: Branched Alkanes,cycloalkanes and aromatic compounds
How is catalytic cracking done in a lab?
Mineral wool is soaked in paraffin and put in a test tube aluminium oxide is added and gas is produced
What is the definition of fuel?
Any substance that releases heat energy when burnt
What is the definition of complete combustion?
Hydrocarbon burns completely in an excess of oxygen producing CO2 and H2O
What is the definition of incomplete combustion?
Limited oxygen means hydrocarbon cannot fully combust producing CO and C
What produces more energy per mole: Complete or incomplete combustion?
Complete combustion
What forms carbon monoxide?
Incomplete combustion
Why is carbon monoxide toxic?
Binds to Haemoglobin meaning less oxygen can be transported round body and causes suffocation
How is sulphur dioxide formed?
Mostly through burning of coal in power stations
How is SO2 dangerous to the environment?
Reacts with atmospheric water to form acid rain
SO2+1/2O2+H2O -> H2SO4
How can SO2 be removed?
Flue gas desulfurisation
How does flue gas desulfurisation work?
CaO or CaO3 is mixed with water to form a slurry
This is sprayed in chimneys
CaO+2H2O+SO2+1/2O2 —> CaSO4 ° 2H20
What is the greenhouse effect?
UV radiation passes from sun to heat earths surface
Earth radiates infrared long wave radiation
The C=O bonds absorb infrared so the radiation cannot escape
Energy is transferred to other molecules through collisions
Surface temperature is rising
What is a free radical?
Any species with an unpaired electron
What is homolytic fission?
UV light causing covalent bonds to break into free radicals
What is a haloalkane?
An alkanes where 1 or more H had been replaced by an alkane
What are the three stages of the formation of haloalkanes?
Initiation,propagation,termination
What does propagation form?
A chain reaction
What is O3 and what does it do?
Ozone
Absorbs harmful UV radiation from the sun
What is damaging about CFC’s?
They destroy the ozone layer
