Reactions of alkenes

What is the functional group of alkenes?

The carbon-carbon double bond.

What does alkenes double bonds allow them to do?

Undergo addition reactions because the double bond can open up and allow the carbons to bond to atoms of another molecule.

What would happen if propene reacted with hydrogen (with a catalyst)?

• The double bond would break.

• The hydrogen atoms will be able to bond to those carbons.

• Forms propane (its alkane). Now saturated.

What conditions are necessary when an alkene reacts with water?

• Catalyst

• High temperatures

What happens when an alkene reacts with water?

• The double bond opens up.

• The water molecule splits into a hydrogen atom and an OH group.

• Both of these can bond to the carbon atoms.

• This product is an alcohol (OH group)

What do we have to do once an alcohol is formed?

Must separate the alcohol from any unreacted ethene and water.

• Ethene is easy as it has a low boiling point. if cooled ethene will remain a gas.

• To separate water and alcohol, fractional distillation is used. Alcohol evaporates first.

What happens when an alkene reacts with a halogen?

• Doesn’t require a catalyst.

• Double bond opens up

• Halogen bonds with the carbons.

What is the most common alkene and halogen reaction?

Ethene + Bromine —> Dibromoethane

This is the test used to identify alkenes. Alkenes decolourise bromine water.

Are alkenes or alkanes more reactive?

Alkenes as they have a double bond.