Alkanes Flashcards
What is the purpose of vacuum distillation?
- Allows heavier fractions to be further separated without high temperatures which could break them down
What is a vacuum distillation unit?
- Heavy residuals from the fractioning column are distilled again under a vacuum
- Lowering the pressure over a liquid will lower its boiling point
What is cracking?
- Conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds
What are the economic reasons for cracking?
- Shorter chain more in demand
- Products of cracking are more valuable then the starting materials
What is fractional distillation in terms of IMF
The splitting of weak van der waals forces between molecules
What are the conditions for thermal cracking?
High pressure (7000 kPa)
High temperature (400-900 Celsius)
What are the products of thermal cracking?
- Produces mostly alkenes
- Sometimes produces hydrogen
What are the conditions for catalytic cracking?
Slight or moderate pressure
High temperature (450 degrees)
Zeolite catalyst
What are the products of catalytic cracking?
Produces branched and cyclic alkanes
Aromatic hydrocarbons
What are the advantages of catalytic cracking?
- 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
What is a fuel?
Releases energy when burnt
What are the products of complete combustion?
CARBON DIOXIDE AND WATER
What are the products of incomplete combustion?
Carbon monoxide and carbon particulates
How is acid rain formed?
- Sulfur containing impurities produce SO2 when burned
- SO2 will dissolve in atmospheric water
How can sulfur dioxide be removed?
- Flue gas desulfurisation
- Acidic sulfur dioxide reacts with calcium oxide in a neutralisation reaction
How is the strong nitrogen bond broken?
- High temperature and spark in the engine provides sufficient energy
What are catalytic converters made of?
- Ceramic honeycomb
- Coated with a thin layer of platinum, palladium & rhodium
- Gives large surface area
What do catalytic converters do?
Remove carbon monoxide, nitrogen oxides and unburned hydrocarbons to turn them into ‘harmless’ carbon dioxide, nitrogen and water
What are the 3 steps of the free radical substitution mechanism?
- Initiation
- Propagation
- Termination
What are free radicals?
A reactive species which has an unpaired electron
Define stereoisomer
Same STRUCTURAL formula different spatial arrangement of atoms
Define homologous series
Same general formula same functional group
Outline the eventual features of the fractional distillation of crude oil that enables the crude oil to be separated into fractions
- Different boiling points in each fraction
- Boiling points depends on chain length
- Temperature gradient
- Cooler at the top of column, hotter at bottom
- The larger the molecule the further down the fraction will be collected
State the meaning of ‘fraction’ in fractional distillation
Mixture of hydrocarbons of similar chain length with similar boiling points
1-5 carbons
Fuel gas - bottled gases
4-12 carbons
Petrol - cars
8-12 carbons
NAPTHA - production of chemicals
11-16 carbons
Kerosene - jet fuel
15- 18 carbons
Diesel - lorries
19 - 35 carbons
Lubricating oil - candles, engine oil
70+ carbons
Residue - tar for roads
Explain why oil companies need to crack large hydrocarbons
- short chain in more demand
- short chain more valuable
Mechanism of greenhouse effect
- UV wavelength radiation passes through atm to Earths surface and heats up surface
- Earth radiates out infrared long wavelength radiation
- The C=O bonds in CO2 absorb infrared radiation so the IR radiation does not escape from atm
- Energy is transferred to other molecules in atm by collisions so atm is warmed
