Organic chemistry Flashcards
What is a hydrocarbon?
any compound formed from ONLY carbon and hydrogen atoms
What are alkanes?
a homologous series which are saturated compounds where each carbon atoms form four single covalent bonds
What is a homologous series?
a group of organic compounds that react in a similar way
What is the general formula for an alkane?
Cn H2n+2
What happens when a hydrocarbon chain becomes shorter?
- becomes more runny and less viscous
- more volatile (lower boiling points)
- more flammable
What is the word equation for the complete combustion of a hydrocarbon?
hydrocarbon+oxygen–> carbon dioxide + water
What is crude oil?
a fossil fuel made up of the remains of plankton
How is crude oil made?
plankton that died millions of years ago were buried in mud and over millions of years, with high temperature and pressure, the remains turn to crude oil, which can be drilled up from the rocks.
What is fractional distillation used for?
to separate hydrocarbon fractions
Describe the process of fractional distillation
- oil is heated until most of it has turned into gas- the gases enter a fractionating column
- in the column there is a temperature gradient (hot at bottom and cool at top)
- The longer hydrocarbons have high boiling points- they condense back into liquids and drain out of the column early on when they are near the bottom Whereas the shorter hydrocarbons condense and drain out much later on at the top of column
- The crude oil mixture will separate out into different fractions
What are the different uses of crude oil?
- provides fuel for modern transport (diesel oil, kerosene, heavy fuel oil and LPG)
- petrochemical industry uses some hydrocarbons from crude oil as feed stock to make new compounds for use in things like polymers. solvents, lubricants and detergents
What is cracking?
the splitting up of long-chain hydrocarbons
Why is cracking useful?
short-chain hydrocarbons are flammable so make good fuels and are in high demand whereas long-chain hydrocarbons form thick gloopy liquids like tar. So, cracking is used to make useful hydrocarbons
What are the different methods of cracking?
- catalytic cracking
- steam cracking
Describe the process of catalytic cracking
- heat long-chain hydrocarbons to vaporise them
- pass the vapour over a hot powered aluminium oxide catalyst
- The long-chain molecules split apart on the surface of the specks of the catalyst
Describe the process of steam cracking?
- mix the long-chain hydrocarbons with steam
- heat them to a very high temperature and they will split into smaller hydro-carbons
What are alkenes?
hydrocarbons which have a double bond between two of the carbon atoms in their chain
are alkenes saturated or unsaturated?
unsaturated because they have fewer hydrogen molecules than alkanes
Why are alkenes reactive?
because the carbon double bond can open up to make a single bond, allowing the two carbon atoms to react with other atoms.
Whats the general formula for alkenes?
CnH2n