Hydrocarbons Flashcards
What is a homologous series?
A family of organic compounds with
- same functional group
- same chemical formula
- similar chemical properties
- gradual change in physical properties
What is the general formula for alkanes?
CnH2n+2
What are the physical properties of alkanes?
Covalent compounds with simple molecular structures
- low m.p. and b.p.
- insoluble in water
- soluble in organic solvents
What are the gradual changes in the alkane homologous series?
- m.p. and b.p. increases
- viscosity increases
Why are alkanes generally unreactive?
They only consists of carbon-carbon single bonds and carbon-hydrogen bonds, these bonds are strong and difficult to break.
What is the equation for complete combustion?
alkane + excess oxygen –> carbon dioxide + water vapour
2 C2H6 + 7 O2 –> 4 CO2 + 6 H2O
What is the equation for incomplete combustion?
alkane + limited oxygen –> carbon monoxide + water vapour
2 C2H6 + 5 O2 –> 4 CO + 6 H2O
What is substitution?
Alkanes react with halogens such as chlorine and bromine in the presence of ultraviolet (UV) light
What is the general formula of alkenes?
CnH2n
What reactions can alkenes undergo?
- Combustion
- Addition
- Addition polymerisation
- Hydrogenation
- Bromination
When does addition polymerisation occur?
When unsaturated monomers join together to form a simgle large molecule (polymer) in the presence of a cataylst and high temperature and pressure
How can margarine be produced?
Adding excess hydrogen to unsaturated vegetable oil at 200 degrees in the presence of nickel cataylst
How can alkenes be obtained?
Cracking petroleum (crude oil)
What are the conditions for cracking?
600 degrees and aluminium oxide cataylst
Why is cracking important?
- produce short-chain alkenes
- produce hydrogen gas (not all cracking reactions produce hydrogen gas)
- produce shorter-chain alkanes such as petrol
