Alkenes Flashcards
(23 cards)
What are alkenes?
Unsaturated hydrocarbons that contain at least one double bond between carbon atoms.
What is the general formula for alkenes?
CₙH₂ₙ
What is the simplest alkene?
Ethene (C₂H₄).
What is the main characteristic of alkenes?
The presence of a carbon-carbon double bond.
How do alkenes differ from alkanes?
Alkenes are unsaturated with a double bond, while alkanes are saturated with single bonds.
What happens in an addition reaction with alkenes?
The double bond in the alkene breaks, and new atoms add to the carbons involved in the double bond.
What is hydrogenation?
The addition of hydrogen (H₂) to an alkene to form an alkane.
What is the catalyst used in hydrogenation?
Nickel or platinum.
What is the product of the reaction between ethene and hydrogen?
Ethane (C₂H₆).
What is halogenation?
The addition of halogens (e.g., Cl₂, Br₂) to alkenes, forming dihalogenated compounds.
What is the test for alkenes?
The bromine water test – alkenes decolorise bromine water.
What happens when alkenes react with bromine?
They form a dihaloalkane, and the bromine water loses its colour.
What is hydration of alkenes?
The addition of water (H₂O) to an alkene in the presence of a catalyst, usually phosphoric acid, forming an alcohol.
What is the product when ethene undergoes hydration?
Ethanol (C₂H₅OH).
What is polymerisation of alkenes?
The process in which many alkene molecules (monomers) join together to form a polymer.
What is the repeating unit in a polymer made from ethene?
–CH₂CH₂–
What is an example of a polymer made from ethene?
Polyethene (used in plastic bags, bottles, etc.).
How is ethene polymerised?
By using heat, pressure, and a catalyst to break the double bond and join monomers together.
What happens when alkenes react with hydrogen halides?
They form a halogenoalkane (e.g., ethene + HCl → chloroethane).
What is the name of the reaction when an alkene reacts with a halogen?
Halogenation.
How do alkenes react with steam?
They form alcohols in the presence of a phosphoric acid catalyst.
What is the product of the reaction between ethene and chlorine?
1,2-dichloroethane.
Why are alkenes more reactive than alkanes?
Because of the electron-rich double bond, which is easily attacked by electrophiles.
