hydrocarbons and crude oil KO Flashcards
What is a hydrocarbon
A molecule that is formed from carbon and hydrogen atoms only.
What is the name given to the simplest hydrocarbon molecules?
Alkanes
Alkanes are said to be saturated. What does this mean?
There are no carbon-carbon double bonds so all the atoms have formed bonds with as many other atoms as they can.
Name and give the formula for the first four alkanes in the homologous series
Methane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
What is the general formula for alkanes?
CnH2n+2
What are the properties of hydrocarbons?
The shorter the molecule is, the runnier the hydrocarbon – the less viscous it is
The shorter the molecules, the lower their boiling point is – the lower the temperature at which they vaporise or condense.
The shorter the molecules, the more flammable the hydrocarbon is
Takes part in combustion reaction
What is the general equation for complete combustion?
Hydrocarbon + Oxygen 🡪 Carbon dioxide + Water vapour
Write a balanced symbol equation for the complete combustion of propane.
C3H8 + 5O2 🡪 3CO2 + 4H20
What is crude oil?
It is a mixture of many different compounds – mostly hydrocarbons with the majority of them being alkanes.
How was crude oil formed?
It was formed from the remain of plants and animals, mainly plankton, that died millions of years ago.
They were buried in mud.
Over millions, of years, with high temperature and pressure, the remains turned into crude oil.
Crude oil is a finite resource. What does this mean?
A finite resource is a resource that isn’t replaced at a quick enough rate to be considered replaceable.
What is another word for finite resource?
Non-renewable resource.
What is the process used to separate crude oil?
Fractional distillation
Describe fractional distillation
The crude oil is first heated so that it vapourises.
It is piped into the fractionating column.
Which has a temperature gradient running through it (hottest at the bottom and coldest at the top).
The gas rises up the column and cools.
Different compounds in the mixture have different boiling points, so they condense at different levels in the fractionating column.
Hydrocarbons that have similar number of carbon atoms have similar boiling points, so they condense at similar levels in the column.
The fractions with similar boiling points are tapped off at the different levels where they condense.
What is crude oil used for?
Fractions from crude oil can be processed to provide fuel for modern transport.
What is meant by a homologous series?
A group of compounds that all have the same general formula with many properties in common.
What is cracking of crude oil?
Cracking is a thermal decomposition reaction.
It is the breaking down of hydrocarbons by heating.
Long chains are broken down into shorter alkanes and alkenes.
What is the purpose of cracking?
To break down the longer more viscous hydrocarbons into shorter alkanes that are in higher demand because they make good fuels.
Name and describe the conditions for two types of cracking.
Catalytic cracking – where hydrocarbon is heated and turned into a vapour which is passed over a hot powdered catalyst (zeolite/aluminium silicate)
Steam cracking – where the vapour is mixed with steam and heated to a very high temperature
What might the equation be for the cracking of decane?
Decane 🡪 Octane + Ethene
Decane 🡪 Hexane + 2xEthene
