Alkanes Flashcards
Why are alkanes almost non-polar?
Because the electronegativities of carbon and hydrogen are so similar.
Why are alkanes soluble in water?
Water molecules are held together by hydrogen bonds which are much stronger than the van der Waals forces holding the alkanes together.
Are alkanes reactive?
No but they burn in oxygen.
Why should sulfur compounds in crude oil be removed before being used for central heating fuel?
From SO2 which contributes to acid rain.
Why are the longer hydrocarbon chains cracked into smaller ones?
The shorter chains are more useful
Some of the products are alkenes which are more reactive than alkanes.
Describe thermal cracking.
Heating alkanes to high temperatures and under high pressures to produce shorter chain molecules which are mostly alkenes.
Describe catalytic cracking.
Lower temperature and a lower pressure using a zeolite catalyst. Produces mostly branched akanes, cycloalkanes and aromatic compounds.
What is produced in complete combustion?
CO2 and water.
What is produced in incomplete combustion?
CO and water.
What is flue gas desulfurisation?
Spraying a surry of CaO and water into the flue gas. Reacts to form calcium sulfite.
What do catalytic converters do?
Reduce the output of CO, nitrogen oxides and unburnt hydrocarbons in the exhaust gas mixture.
What is the catalyst found in a catalytic converter?
Platinum and rhodium metals.
Name the three stages in free-radical substitution.
Initiation, propagation and termination.
What happens in propagation?
Free-radical reacts with the alkane, produces a stable compound and a radicalised methyl group, this reacts with the start halogen to form another stable compounds and a halogen free-radical.
Give an example of free-radical substitution in the atmosphere?
Chlorine free radicals decompose ozone into oxygen.
