ORGANIC CHEMISTRY Flashcards
WHAT IS a hydrocarbon
a compound that only contains hydrogen and carbon atoms
what is an alkane
they are saturated hydrocarbons
and they have carbon carbon single bonds
what are the first four alkanes
methane
ethane
propane
butane
what is the general formula for alkanes
CnH2n+2
what happens if you change the length of a carbon chain
the properties of the hydrocarbon change
properties of short hydrocarbons
less viscous
more volatile (lower boiling point)
more flammable
what are the products of the complete combustion of any hydrocarbon
carbon dioxide and water
what can hydrocarbons be used as
they can be used as fuels because of the energy that they release when they combust completely
complete combustion equation
hydrocarbon + oxygen ——- carbon dioxide + water
what is crude oil
it is fossil fuel and contains a mixture of hydrocarbons
how are the different compounds in crude oil seperated
fractional distillation
how does fractional distillation work
the oil is heated until most of it has turned into a gas, the gases then enter a fractionating column
in the column theres a temperature gradient
the longer hydrocarbons have high boiling points, they condense back into liquids and drain out of the column early on, when theyre near the bottom
the shorter hydrocarbons have lower boiling points they condense and drain near the top of the column where its cooler
the crude oil mixture is now separated into different fractions
importance of crude oil
oil provides the fuel for most modern transport
the petrochemical industry uses some of the hydrocarbons from crude oil as feedstock to make new compounds for use in things like polymers solvents lubricants and detergents
what is cracking
splitting up long chain hydrocarbons
why would we crack longer chain hydrocarbons
longer chain hydrocarbons form thick gloopy liquids which aren’t useful and short hydrocarbons are more useful as they are more flammable, so they make good fuels and are in high demand
why is cracking useful
longer hydrocarbon molecules produced from fractional distillation are turned into smaller more useful ones by cracking
what type of reaction is cracking
thermal decomposition reaction
process of catalytic cracking
the first step is too heat long chain hydrocarbons to vaporise them
then the vapour is passed over a hot powdered aluminium oxide catalyst
the long chain molecules split apart on the surface of the specks of catalysts
whats another way of cracking hydrocarbons other than catalytic cracking and how does it work
steam cracking
if you vaporise them mix them with steam and then heat them to a very high temperature
What are alkenes
they are unsaturated hydrocarbons
and they have double carbon carbon bonds
what are the first 4 alkenes and how many c’s does it have
ethene (2cs)
propene (3cs)
butene (4cs)
pentene (5cs)
what is the general formula for alkenes
CnH2n
in a large amount of oxygen, alkenes…..
combust completely to produce only water and carbon dioxide
why is it hard for alkenes to combust completely what happens when this happens
there isn’t enough oxygen in the air for this, so when you burn them they tend to undergo incomplete combustion
