Organic - Alkanes Flashcards
what is crude oil?
a mixture of different hydrocarbons
why can crude oil be separated into the separate molecules by fractional distillation?
as the different chains lengths of molecules result in them having different boiling points
by what process can crude oil be separated into the separate molecules?
fractional distillation
how does the temperature change moving up a fractioning column?
it is hottest at the bottom and cooler at the top
where in the column do shorter chain hydrocarbons condense? why?
high up the column because they have lower boiling points
where in the column do longer chain hydrocarbons condense? why?
nearer the bottom because they have lower boiling points
after fractional distillation, what happens to the products to break them down further?
cracking
why are hydrocarbons cracked?
to turn longer carbon chains into more useful smaller molecules
why are harsh reaction conditions required for cracking?
because C-C bonds are broken
what are the 2 main types of cracking?
thermal cracking
catalytic cracking
what are the main products of thermal cracking?
high proportion of alkanes and alkenes
what are the conditions for thermal cracking?
high temperature (around 1200 K)
high pressure (around 7000 kPa)
what are the main products of catalytic cracking?
aromatic compounds with carbon rings
what are the conditions required for catalytic cracking?
lower temperatures (than thermal) (around 720 K)
normal pressure
zeolite catalyst
why do alkanes make good fuels?
they release a lot of energy when burned
with sufficient oxygen, how do alkanes combust? what are the products?
completely
carbon dioxide and water
with insufficient oxygen, how do alkanes combust? what are the products?
incompletely
carbon monoxide and water
what harmful by-products of combustion are removed by a catalytic converter?
carbon monoxide
oxides of nitrogen
what metal is the catalyst in a catalytic converter?
rhodium or platinum
what does a catalytic converter convert harmful products into?
more stable ones such as CO₂ or H₂O
what are carbon particulates?
small fragments of unburned hydrocarbon
how are carbon particulates harmful?
respiratory problems
atmospheric pollutant
how are sulphur impurities harmful?
react in the air leading to the acidification of water in the atmosphere, forming a weak form of sulphuric acid, acid rain
by what process can sulphur impurities be removed from waste products after combustion?
flue gas desulphurisation
how are halogenoalkanes produced?
alkanes reacting with halogens in the presence of UV light
what are the 3 steps of chlorination of alkanes?
initiation, propagation, and termination
