Alkenes

Alkenes have a C=C double bond

• Means that alkenes have two fewer hydrocarbons
• They are unsaturated as they contain the same number of hydrogen and carbon atoms, unlike alkanes which are saturated as they contain different amounts of hydrogen and carbon
• Bond can open, allowing the two carbon atoms to bond with other atoms, which makes them far more reactive than alkanes
• First four are ethene, propene, butene, pentene

Alkenes burn with a smokey flame

• Alkenes normally combust completely if there’s enough oxygen
• However, there isn’t enough oxygen in the air of this, so they undergo incomplete combustion
  • Alkenes + oxygen - carbon + carbon monoxide + carbon dioxide + water(+energy)
  • Result in a smokey yellow flame and less energy being released