Flashcards in 6.2 - Hydrocarbons/ Alkanes, Alkenes Deck (37)
What are Alkanes?
what re Alkenes?
Alkanes general formula?
Alkenes general formula?
=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'
a catalyst is used together with high temperature
useful, break down hydrocarbons to make more useful fuels
temperature and pressure
catalyst, temperature, pressure
Inject crude oil
collected as fractions
What is the point in burning alkanes?
To make useful substances such as petrol and diesel
Free radical substitution steps?
What are the conditions needed for homolytic fission?
the molecule is split by homolytic fission, forming 2 radicals
during the halogenation of alkanes, the radical will then go onto react with eg. methane
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
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
When is a pi bond formed?
when 2 p orbitals overlap sideways, it forms an area above and below the molecular axis.
which bond is weaker?
pi bond is MUCH weaker
Why do trans isomers have lower boiling points?
Because the U shape of the cis isomer doesnt pack as well as the straighter shape. Intermolecular forces arent as strong as they should be
Making alkanes from alkenes?
is the breaking of a covalent bond so that both bonding electrons are taken by one atom