ORGANIC - ALKANES Flashcards
What is an alkane?
Saturated hydrocarbons that only contain C-C and C-H bonds
Alkanes physical properties
POLARITY - almost non polar as the electronegativities of carbon and hydrogen are so similar.
BOILING POINTS - increasing IMF so the bp of alkanes increases as chain length increases. Branched chains have lower mp then straight with same num of carbons - cant pack togehter as close so VdW not as effective
SOLUBILITY - Insoluble in water as water molecules are held together by H bonds which are stronger than VdW forces between alkane molecules
Describe fractional distillation
Crude oil made of diff hydrocarbons and can be separated by fractional distillation.
STEPS:
1. Mixture is vapourised and fed into fractioning column
2. Vapours rise cool and condense
3. Products are siphoned off for different uses
- Short chains : low bp : rise higher : condense at top
What is petroleum
A mixture consisting mainly of alkane hydrocarbons that can be separated by fractional distillation
Why is cracking used
Longer carbon chains aren’t useful so they are broken down to form smaller more useful molecules (economic benefits)
The c-c bonds are broken in order to do this
Describe thermal cracking
Takes place at high pressure and high temperature and produces a high percentage of alkanes
Describe catalytic cracking
Slight pressure, high temperature and in the presence of a zeolite catalyst and is used mainly to produce fuels and aromatic hydrocarbons
Describe complete combustion
Alkanes are good fuels as they release lots of energy when burned
Sufficient oxygen present they undergo complete combustion - carbon dioxide + water
Describe incomplete combustion
Insufficient oxygen then incomplete combustion
Carbon monoxide + watet
- less oxygen = soot
Purpose of catalytic converters
Carbon monoxide (toxic) and oxides of nitrogen are by products of alkane combustion
- Both gases removed using catalytic converter which uses a rhodium catalyst to convert harmful products into more stable ones like CO2 and H2O
Purpose of flue gas desulfurisation
Sulfur impurities lead to acidification of water in earth’s atmosphere as they react to form weak H2SO4
- Impurities can be removed from waste products via flue gas desulfurisation the gases pass through a scrubber containing calcium oxide and gypsum which reacts with the acidic súlfur dioxide in a neutralisation reaction
SO2 + CaO —> CaSO3 ( calcium sulfite produced can be used to make calcium sulfate for plasterboard
explain why sulfur dioxide can be removed from flue gases using calcium oxide or calcium carbonate.
-Powdered calcium carbonate (limestone) or calcium oxide is mixed with water to make an alkaline slurry.
When the flue gases mix with the alkaline slurry, the acidic sulfur dioxide gas reacts with the calcium compounds to form a harmless salt (calcium sulfate).
CaO + SO →CaSO (s) 2(g) 360
What is chlorination of alkanes?
Alkanes react with halogens in the presence of UV light to produce halogenoalkanes.
- UV light breaks down the halogen bonds producing free radicals these attack the alkanes resulting in a series of reactions
- initiation
- propagation
- termination
What is initiation
halogen is broken down
What is propagation
A hydrogen is replaced and the CL. radical is reformed as a catalyst
- Propagation can continue many times to result in multiple substitution (chain reaction)
