Alkanes Flashcards
What is the general formula for an alkane?
C nH 2n +2
What is rude oil?
A mixture of different hydrocarbons
Which chains are in higher demand?
Short chains
What type of fractions do you find near the top of the distillation column?
Fractions of molecules with lower boiling points and shorter chains
Where is LPG found in the fractionation column?
Near the top
Give examples of fractions collected before diesel
[2]:
- Kerosene
- Petrol
What decreases as you go down the fractionation column [2]:
Flammability and volatility of chains
What increases as you go down the fractionation column?
Viscosity
Where would you be likely to find bitumen on the fractionational distillation column?
Near the bottom
What is petroleum?
Petroleum is a mixture consisting mainly of alkane hydrocarbons
What is a petroleum fraction?
Petroleum fraction: mixture of hydrocarbons with
a similar chain length and boiling point range
Industrial fractional distillation procedure [4]:
- Oil is pre-heated then passed into column.
- The temperature of column decreases upwards
- The fractions condense at different heights
- The separation depends on boiling point which depends on size of molecules
In Industrial fractional distillation the larger the molecule the larger the…
Van der waaals forces
Industrial fractional distillation is a process that…
involves the splitting of weak van der waals forces
between molecules
Vacuum distillation unit [3]:
- Heavy residues from the fractionating column are distilled again under a vacuum.
- Lowering the pressure over a liquid will lower its boiling
point. - Allows heavier fractions to be further separated without high temperatures which could break them down
Fractional Distillation in the laboratory [3]:
- Vapours pass up the fractionating column the vapour with the lower boiling point reaches the top of the fractionating column first.
- The vapours with higher boiling points condense
back into the flask - Only the most volatile vapour passes into the
condenser
Where should the thermometer be during fractional distillation in the laboratory?
thermometer should be at or below the boiling
point of the most volatile substance
What does the condenser do during fractional distillation in the laboratory?
The condenser cools the vapours and condenses to
a liquid and is collected
What is fractional distillation in the laboratory used for?
To separate liquids with different boiling points
Cracking [definition]:
conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds
Cracking advantages [3]:
- petroleum fractions with shorter carbon chains are in more demand than larger fractions
- make use of excess larger hydrocarbons
- The products of cracking are more valuable than the starting materials
What does thermal cracking produce? [2]:
- produces mostly alkenes
- sometimes produces hydrogen
Conditions for thermal cracking [2]:
- High pressure (7000 kPa)
- High temperature (400°C to 900°C)
What is catalytic cracking used for?
Making motor fuels
What does catalytic cracking produce? [2]:
- branched and cyclic alkanes
- aromatic hydrocarbons
Advantages of catalytic cracking [2];
- Branched and cyclic hydrocarbons burn more
cleanly and are used to give fuels a higher octane
number - Cheaper than thermal cracking because it saves
energy as lower temperatures and pressures are used
Combustion of alkanes [2]:
- Alkanes readily burn in the presence of oxygen
- This combustion of alkanes is highly
exothermic
What are the harmful products of incomplete combustion [2]:
- CO is toxic
- Carbon (soot) can cause global dimming- reflection of the sun’s light
Combustion equation:
x + O2 = CO2 + H2O
Catalytic converters [2]:
- Converters have a ceramic honeycomb coated with a thin layer of catalyst metals
- Turn molecules produced in car engines into relatively less harmful ones
What are the catalyst metals on catalytic converters?
[3]:
- platinum
- palladium
- rhodium
Why do catalytic converters have a large honeycomb structure?
to give a large surface area
Catalytic conversions [2]:
- 2 CO + 2 NO → 2 CO2 + N
- S + O → SO2
Why is CO harmful?
Toxic
Why is CO2 harmful?
Greenhouse gas- contributes to global warming
Why is NO2 harmful?
NO is toxic and can form acidic gas NO2 which is toxic and acidic, forms acid rain
Why is Sulphur harmful?
Form SO3 in atmosphere which dissolves in water and forms acid rain
What happens when alkanes react with bromine/ chlorine under UV light?
- Free radical substitution
- Produces halogenoalkanes
Mechanism of greenhouse effect [4]:
- UV wavelength radiation passes through atmosphere to Earth’s surface and heats up surface
- The Earth radiates out infrared long wavelength radiation
- The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere
- This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed
Free radical [definition]:
A reactive species which possess an unpaired electron, represented by a dot
Initiation:
Free radical on products side
Propagation:
Free radical on products and reactants
Termination:
Free radical on reactants side
What are the conditions for free radical substitution?
[3]:
- UV light
- Alkene present
- Halogen present
