Reaction of alkenes

• Why are alkenes more reactive than alkanes

  Have a carbon double bond which is very reactive
• What chemical test can be used to distinguish alkenes from alkanes

  Add orange bromine water to unknown alkane or alkene and shake

  If it’s added to a saturated compound like alkane it will remain orange
• What type of reaction can an alkene be part of because of the carbon double bond

  Addition reactions
• How do addition reactions work

  When two molecules combine to form a single molecules the carbon double bond breaks and opens up them a new atom is added to each carbon
• Hyrdrogenation

  Addition of hydrogen to an alkene in the presence of a catalyst forming an alkane
• How does hydrogenation work

  An alkene reacts with hydrogen in the presence of a catalyst

  This gets rid of the double bond and adds a hydrogen to each catalyst
• How do alkenes form alcohols

  They react with steam in the presence of a catalyst

  This breaks the double bond with hydrogen going on one side and OH going on the other

  We then have to separate out the alcohol
• What happens when alkenes react with halogens

  The double bond will break and each carbon will bond to a halogen atom
• Do alkanes tend to undergo complete or incomplete combustion

  Usually combust completely
• Do alkenes often undergo complete or incomplete combustion

  Often undergo incomplete combustion
• Incomplete combustion

  Combustion without sufficient oxygen to react completely
• Drawbacks of incomplete combustion

  A smoky yellow flame

  Less energy is released than from complete combustion

  Produces pollutants
• What harmful products can be produced by the incomplete combustion of hydrocarbons

  Carbon

  Carbon monoxide

  Unburnt hydrocarbons