GCSE Chemistry (AQA)

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Reactions of Alkenes

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Organic chemistry Reactions of alkenes and alcohols

Reactions of Alkenes

9:49 Alkenes: Structure, Formula, and Reactions
Spec 4.7.2.2
Previous Alkene Names & Formulae Next Alcohol Names & Formulae
  • Alkenes react with hydrogen, halogens, and water in addition reactions.
  • Alkenes have a carbon-carbon double bond.
  • Hydrogen exists as H2, water as H2O, and halogens as diatomic molecules.
  • Halogens are in group seven of the periodic table, including chlorine, bromine, and iodine.
  • In addition reactions, atoms are added across the carbon-carbon double bond.
  • Example: Ethene (C2H4) reacts with hydrogen (H2) to form ethane (C2H6).
  • The double bond becomes a single bond, allowing each carbon to form three other bonds.
  • Alkenes react with hydrogen when heated with a catalyst, often metals like nickel or platinum.
  • Catalysts lower the activation energy of the reaction.
  • Temperatures above 300 degrees Celsius are needed for the reaction.
  • The addition of hydrogen to an alkene produces an alkane, which is saturated.
  • Alkenes react with halogens in similar addition reactions, forming diatomic molecules with carbon atoms.
  • Example: Ethene reacts with chlorine to form C2H4Cl2.
  • Bromine water turns colorless when reacting with alkenes, indicating the presence of an alkene.
  • Alkenes react with water in the form of steam, producing alcohols.
  • Example: Butene reacts with water to form butanol.
  • Alkenes undergo combustion reactions with oxygen, often resulting in incomplete combustion with smoky flames.
  • Incomplete combustion occurs due to insufficient oxygen, producing carbon monoxide or soot.
  • Example: Ethene reacts with oxygen to form carbon monoxide and water or carbon (soot) and water.

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