Alkenes are a different homologous series of hydrocarbons. However, unlike alkanes, alkenes have a double covalent bond between two carbon atoms, so they are not saturated.
The general formula for alkenes is CnH2n
They have similar properties to alkanes (ethene, propene and butene are gases), however, alkenes react differently to alkanes because the double bond between the carbons breaks so more atoms can be added to the molecule.
Combustion - C2H4(g) + 3O2(g) -> 2CO2(g) + 2H2O(l)
The Addition of Bromine - CH2=CH2(g) + Br2(aq) -> CH2BrCH2Br(l)
- ^ The alkene can be written like this to represent the actual structure.
- The double bond breaks and joins with bromine.
- The product is a colourless liquid called 1,2-dibromoethane.
- This reaction is used to test for a double bond because an alkane wouldn't react with it so the bromine brown colour would be visible, but with an alkene the solution turns colourless.
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