ORGANIC CHEMISTRY Flashcards
(15 cards)
What is crude oil?
Crude oil is a mixture of compounds it is a finite resource of energy and is a fossil fuel from ancient biomass
What is a hydrocarbon?
A hydrocarbon is a compound made out of hydrogen and carbon atoms
What are Alkanes?
Alkanes are saturated hydrocarbons (contain only single bonds) with a general formula of CnH2n+2
What is a homologous series?
A homologous series is a series of compounds made up of the same general formula, same functional group and contains similar chemical properties.
Describe the combustion of hydrocarbons.
-An exothermic reaction is occurring when hydrocarbons are reacted with oxygen
-During complete combustion there will be a sufficient amount of oxygen supply producing carbon dioxide and water as products(carbon and hydrogen will be completely oxidised).Energy is released as heat and light. The flame is typically blue.
-During incomplete combustion there would be an insufficient supply of oxygen resulting in the production of carbon or carbon monoxide and water. less energy is produced and the the flame colour produced is yellow or orange.
Describe the change in physical properties of Alkanes (hydrocarbons) as the chains get longer
- The bigger the hydrocarbon chain the more viscous (thick) it is.
- As the chains get bigger so does the boiling points as it becomes less volatile (easily evaporated)
- The bigger the chain the less flammable (ignitable) it is
- The properties of hydrocarbons effect how its used for fuels e.g. short hydrocarbon chains with lower boiling points are used as 2bottled gases” stored under pressure as liquids in bottles
- Alkanes have poor reactivity
- In alkanes the series go from gases to liquids then to solids
Explain how fractional distillation of crude oil occurs
1) Crude oil is heated and evaporated
2) water rises up the fractionating column
2) The column has a temperature gradient it is hotter at the bottom and cooler at the top.
3) The longer hydrocarbons have a high boiling point and they condense into liquids and drain out of the column at the bottom as the temperature there, while still high, is not high enough to keep them in vapor form.
4) The shorter hydrocarbons have low boiling points they condense and drain out at the top of the column where it is cooler as they stay vapour at the bottom but condense at the top where it is cooler.
5) This gives fractions where each fraction contains a mixture of hydrocarbons that contain similar boiling points
what is cracking?
Cracking is when large hydrocarbons are thermally broken down into smaller and more useful hydrocarbons.
What type of reaction is cracking?
Thermal decomposition reaction.
What are the conditions for cracking?
During catalytic cracking
1. Heat the long-chain hydrocarbon to vaporise them
2. The vapour is passed through a hot powdered aluminium oxide catalyst
Or During steam cracking
1. Vaporise the long hydrocarbon chain
2. mix the vapour with steam and then heat them to a very high temperature
What are the products of cracking and how are they used?
The products are alkanes and alkenes which can be used as starting material for synthesis and making polymers.
What tis an alkene?
An alkene is an unsaturated hydrocarbon containing double carbon bonds and its general formula is CnH2n
with the four four alkenes being ethene with 2c/ propane with 3c / butene with 4c/ pentene with 5c
What is the test for alkenes?
When an alkene is added to bromine water the bromine water changes from an orange colour to colourless
Describe the combustion of alkenes
As there isn’t much oxygen in air alkenes tend to undergo incomplete combustion resulting them to burn with a smoky flame and producing carbon and carbon monoxide which is a poisonous gas as products.
