Types of Alkene Reactions
Chemistry: AQA GCSE Higher, topic 7.2.4
Examples of Alkene Addition Reactions
Alkenes are involved in addition reactions with different substances:
Alkenes and oxygen
- Alkenes can be involved in combustion reactions with oxygen. The outcome of these reactions is similar to when other hydrocarbons react with oxygen.
- E.g. Ethene (C2H4) + oxygen (O2) → carbon monoxide (CO) + carbon (C) + water (H2O)
- Because their combustion is incomplete, they burn with smoky flames.
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Alkenes and hydrogen
- When a nickel catalyst is present, alkanes can be formed by combining hydrogen with an alkene.
- E.g. Ethene (C2H4) + hydrogen (H2) → ethane (C2H6)
- Adding hydrogen atoms across a carbon-carbon double bond is called hydrogenation.
Alkenes and water
- When a phosphoric acid catalyst is present, alcohols can be formed by reacting alkenes with steam.
- E.g. Ethene (C2H4) + steam (H2O) → ethanol (C2H5OH)
Alkenes and halogens
- Alkenes, unlike alkanes, will react if mixed with bromine water and shaken. This causes the solution to change colour from orange-brown to colourless.
- E.g. Ethene (C2H4) (colourless) + bromine (Br2) (orange-brown solution) → dibromoethane (CH2BrCH2Br) (colourless)
- This is an effective test for distinguishing between alkenes and alkanes.
Test yourself on Types of Alkene Reactions
A student shakes two hydrocarbons separately with bromine water. Only one sample turns the bromine water colourless. What does this show about that sample?
What is the name of the process of adding hydrogen atoms across a carbon-carbon double bond?
For alkenes to react with water, you need...
What must be reacted together to give dibromoethane?
What three products are formed when ethene undergoes incomplete combustion with oxygen?