All alkenes in the alkene homologous series have the same functional group. This means they all have at least one C=C double bond, which makes them react in similar ways. In a reaction, this double bond can break open, allowing the carbon atoms to attach to something new. This type of reaction is called an addition reaction because something is added to the alkene.

• No other products are formed during this process.

Alkenes can react with hydrogen to form an alkane, in a process called hydrogenation Alkene + Hydrogen → Alkane

These reactions require a catalyst. An example of a hydrogenation reaction is: Ethene + Hydrogen → Ethane

In the presence of heat, alkenes can react with steam to form an alcohol in a process called hydration

These reactions require a temperature of around 300°C, a pressure of around 60 – 70 atm and a catalyst.

An example of a hydration reaction is:

Alkenes can also react with halogens, such as chlorine, in a process called halogenation:

An example of a halogenation reaction is: