6.2 - Hydrocarbons/ Alkanes, Alkenes Flashcards
What are Alkanes?
SATURATED hydrocarbons
what re Alkenes?
UNSATURATED hydrocarbons
Alkanes general formula?
CnH2n+2
Alkenes general formula?
CnH2n
Octane numbers?
=A measure of the performance of the fuel
=higher octane means a more efficient fuel
=straight chains are prone to knocking, exploding due to activation energy
=knocking is increased by straight chained hydrocarbons, therefore branched molecules burn better ‘higher octane number’
Reforming?
a catalyst is used together with high temperature
Cracking?
useful, break down hydrocarbons to make more useful fuels
thermal cracking?
temperature and pressure
Catalytic cracking?
catalyst, temperature, pressure
Burning alkanes?
Fractional distillation
Fractional distillation?
Inject crude oil vapourised rises cools condenses collected as fractions
What is the point in burning alkanes?
To make useful substances such as petrol and diesel
Free radical substitution steps?
Initiation
Propagation
Termination
What are the conditions needed for homolytic fission?
U.V light
300 degrees
Initiation?
the molecule is split by homolytic fission, forming 2 radicals
Propagation?
during the halogenation of alkanes, the radical will then go onto react with eg. methane
Rapid process
Termination?
the end of radical substitution where 2 radicals combine to form a molecule
Problems with free radical substitution?
other radicals can be formed
if there’s too much mixture, other products will be formed and therefore have to be separated
Catalytic converters?
Redox reaction
one reduction catalyst and one oxidation
Molecules bond with the catalyst and elements separate off as a harmless gas
Testing for alkenes?
place sample in test tube with drops of bromine water, the more drops needed to go colourless, the more unsaturated
Why are alkenes insoluble in water?
They cant form H bonds because there are no oxygens
Name the 2 bonds in alkenes?
Sigma and pi
When do bonds form?
bonds form between atoms when atomic orbitals overlap and form molecular orbitals
When is a sigma bond formed?
when 2 s orbitals overlap (in a straight line) which is a single covalent bond
