Addition Reactions (Cambridge (CIE) IGCSE Chemistry)

Addition reactions

Extended tier only

• Alkenes undergo addition reactions in which atoms of a simple molecule add across the C=C double bond

• In an addition reaction, only one product is formed

Alkenes and bromine

• The reaction between bromine and ethene is an example of an addition reaction

• The two bromine atoms add across the carbon-carbon double bond to form a saturated compound

• Bromine water is orange but would decolourise when added to an alkene 

Bromine atoms add across the C=C in the addition reaction of ethene and bromine

Alkenes and hydrogen

• When alkenes undergo addition reactions with hydrogen, an alkane is formed

• This reaction requires a nickel catalyst

• The reaction between ethene and hydrogen would produce ethane, propene and hydrogen would form propane and so on 

The hydrogen adds across the carbon carbon-double bond

 Alkenes and steam

• When alkenes undergo addition reactions with steam, an alcohol is formed.

• Since water is being added to the molecule it is also called a hydration reaction 

• This reaction requires an acid catalyst

• Ethene would react with steam to produce ethanol, propene will react with steam to produce propanol and so on

A water molecule adds across the C=C in the hydration of ethene to produce ethanol