C9 Flashcards
What is a hydrocarbon?
Any compound that is formed from carbon and hydrogen atoms only .
What are alkanes?
- Simplest type of hydrocarbon
- a homologous series
- saturated compounds
What is the general formula for an alkane?
CnH2n+2
What is a homologous series?
A group of organic compounds that react in a similar way
Why are alkanes saturated compounds ?
Each carbon atom forms four single covalent bonds
What are the first four alkanes?
- methane
- ethane
- propane
- butane
How can alkane molecule be represented ?
In a H and C diagram or in an equation
How does the length of carbon chain change the properties of the hydrocarbon chain?
- the shorter the carbon chain , the more runny a hydrocarbon is , the less viscous
- hydrocarbons with shorter chains are also more volatile , have lower boiling points
- also shorter carbon chains means they are more flammable
What happens in complete combustion of any hydrocarbon in oxygen?
- releases lots of energy
- waste products of water vapour and carbon dioxide
- both carbon and hydrogen from the hydrocarbon are oxidised
What are hydrocarbons used for?
Fuels due to the amount of energy released when they combust completely
What is crude oil?
Finit resource found in rocks . It is the remains of an ancient biomass consisting mainly of plankton that was buried in the mud
What does crude oil mainly consist off?
Hydrocarbons
What is crude oils state?
Mixture of compounds
What is the equation for the complete combustion of a hydrocarbon?
Hydrocarbon + oxygen —-> carbon dioxide + water
What can change depending on the size of the hydrocarbons molecules ?
- boiling point
- viscosity
- flammability
What does the flammability , viscosity and boiling determine?
How the hydrocarbon will be used as a fuel
How is crude oil separated ?
Fractional distillation
How does fractional distillation work?
- Oil is heated until most has turned to gas. Gas enters fractionating column and liquid bit is drained off
- in column there is a temperature gradient ( hot at bottom and cooler as you go up)
- Longer hydrocarbons have high boiling points. They condense back to liquids and drain out of the column early on. The shorter chains have low boiling points and drain out later on, near the top where it is cooler.
- separated crude oil into fractions . Each fraction contains a mixture of hydrocarbons that contain a similar number of carbon atoms , so similar boiling points
What does oil do for us in our daily lives?
Provides fuel for most modern transport . Diesel oil , kerosene, heavy fuel oil and LPG (liquid petroleum gas ) all come from crude oil
What is the petrochemical industry?
Use hydrocarbons from crude oil , as feed stock to make new compounds for use in things like polymers, solvents , lubricants and detergents
What are the products from crude oil and example off?
Organic compounds. Compounds containing carbon atoms
Why do you get such a large variety of products from crude oil?
Can bond together to form different groups called homologous series . These groups contain similar compounds with many properties in common . Alkanes and alkenes are examples of these
Why do people want smaller chained hydrocarbon?
Flammable and can make good fuels and are in high demand. Long chains on the other hand are thick gloopy liquids like tar that are not useful
How are longer hydrocarbons formed from fractional distillation turned into more useful smaller ones?
Cracking
What are the products of cracking used for?
Fuels
What does cracking produce?
Alkanes and alkenes
What are alkenes?
A lot more reactive alkanes . They are used as a starting material when making other compounds and can be used to make polymers
How can you test for alkenes ?
Bromine water. Orange bromine water is added to an alkane , no reaction will happens and it’ll stay bright orange.
If its added to an alkene the bromine reacts with it to make a colourless compound - so bromine water is decolourised
What type of reaction is cracking?
Thermal decomposition
What is thermal decomposition?
Breaking molecules down by heating them
How to catalytic crack ?
- heat long chain hydrocarbon to vaporise them
- then vapour is passed over a hot powdered aluminium oxide catalyst
- the long chain molecules split apart on the surface of the specks of the catalyst
What is steam cracking?
Vaporise long chain hydrocarbon , mix them with steam , then heat them to a very high temperature
