Chemistry Topic 7//Hydrocarbons//Fractional Distillation/Cracking of Crude Oil Flashcards
What is a HydroCarbon
any compound that is formed from Hydrogen and carbon only
What are 3 facts about Alkanes
- Saturated
- Homologous series
- C-C single bonds
What is an Alkane
A type of HydroCarbon which has C-C single bonds
Why are alkanes Homologous series
Because Alkanes are a group of organic compounds that have similar reactivities
Why are Alkanes Saturated
Because each carbon atoms forms four single covalent bonds
What is the formula of Alkanes
CnH2n+2
What is the first four alkanes and their formula
Methane - CH4
Ethane - C2H6
Propane - C3H8
Butane - C4H10
The shorter the carbon chain of HydroCarbons ….
- The more runny the hydrocarbon is
- The more flammable it is
- The more volatile it is (turns into gas at lower temp)
- lower boiling point
why is shorter chain hydrocarbon in more demand
they burn more efficiently (very flammable) and make better fuels than long hydrocarbons
Describe what happens when complete combustion occurs with hydrocarbon
complete combustion with hydrocarbon with oxygen releases lots of energy but produces waste product like carbon dioxide and water
What oxidises in this complete combustion of hydrocarbon and oxygen
carbon and hydrogen are oxidised and gains oxygen
Why are hydrocarbons used as goof fuels
Due to the amount of energy released when they combust completely
What is crude oil
made up of different hydrocarbons made over long period of time from remains of plants and animals mainly plankton that can be used as fuels
How is crude oil separated by fractional distillation
- The oil is heated until majority is turned into gas
- Gases enter fractionating column where there is a temperature gradient (hot at bottom and cooler at top)
- The longer hydrocarbons have high boiling points and condense back into liquids and drain out
- the shorter hydrocarbons have low boiling points and condense and drain out much later on near top where it is cooler
Explain why different fractions exit the column at different points
Inside fractionating column is a temperature gradient with hottest part at bottom and coolest at top. when hydrocarbons in the crude oil gas reach a part of the column where the temperature is lower than their boiling point, they will condense and drain out of column
What are the 2 main uses of crude oil
- Oil provides fuel for transport vehicles
- Making of new compounds for use in things like polymers, solvents, detergents and lubricants
What is Cracking
Thermal decomposition reaction which consists of splitting up long chain hydrocarbons
Why is cracking useful
Long chain hydrocarbons are useless as they form thick gloopy liquids like tar and instead, short chain hydrocarbons are flammable so make good fuels and in high demand so is useful
What does Cracking produce
Alkane and Alkenes
What are the 2 methods of Cracking
Catalytic cracking
Steam cracking
Describe Catalytic cracking
- Apply heat to long chain hydrocarbon to vaporise them
- The vapor can be passed over a hot powdered aluminium oxide catalyst
- The long chain hydrocarbon splits apart into shorter chain of hydrocarbon made of an alkane and alkene
Describe what happens in steam cracking
- Heat a long chain of hydrocarbon to vaporise them
- Then mix them with steam and then heat them to a very high temperature
- The long chain hydrocarbon splits apart into shorter chain of hydrocarbon made of an alkane and alkene
