Cracking & Alkenes

• What is crude oil primarily composed of?

  A mixture of different hydrocarbons
• What process is used to separate hydrocarbons by the length of their carbon chains?

  Fractional distillation
• Why are shorter hydrocarbons considered better fuels?

  They are more flammable
• What is the purpose of cracking in hydrocarbon processing?

  To break down longer hydrocarbons into shorter, more flammable ones
• What type of reaction is cracking classified as?

  A thermal decomposition reaction
• What does the term "thermal" refer to in thermal decomposition?

  Heating
• What does "decomposition" mean in the context of thermal decomposition?

  Breaking down molecules
• What are the two methods of cracking mentioned?

  Catalytic cracking and steam cracking
• What is the first step in both catalytic and steam cracking?

  To heat and vaporize long chain hydrocarbons
• What catalyst is used in catalytic cracking?

  Hot powdered aluminium oxide
• What happens to long hydrocarbons in catalytic cracking when they contact the catalyst?

  They split apart into two smaller hydrocarbons
• In steam cracking, what is mixed with the vaporized hydrocarbons?

  Steam
• What is the result of heating vaporized hydrocarbons in steam cracking?

  Long hydrocarbon chains split apart into shorter ones
• What is the general equation for the cracking of long chain alkanes?

  Long chain alkane → Shorter alkane + Alkene
• If decane is cracked, what are the products formed?

  A shorter alkane and an alkene
• How do you determine the number of carbons and hydrogens in the unknown alkane when cracking decane?

  Subtract the number of carbons and hydrogens in the known product from those in decane
• What is the formula for the unknown alkane when decane is cracked into ethene?

  C$_8$H$_<18$
• What is a homologous series?

  A group of similar compounds with similar properties
• What is the structural difference between alkenes and alkanes?

  Alkenes have a double bond, while alkanes have only single bonds
• Why are alkenes considered unsaturated?

  They contain double bonds
• What is one important feature of alkenes compared to alkanes?

  Alkenes are more reactive than alkanes
• What happens when bromine water is added to a solution of alkenes?

  It decolorizes from orange to colorless
• What does the decolorization of bromine water indicate?

  It is a test for alkenes
• How can alkenes be used in polymer production?

  Double bonds can break to form two more bonds
• What are the key steps in the cracking process of hydrocarbons?

  1. Heat and vaporize long chain hydrocarbons
  2. For catalytic cracking, pass vapor over a catalyst (aluminium oxide)
  3. For steam cracking, mix vapor with steam and heat
  4. Split long hydrocarbons into shorter ones
• What are the properties and reactions of alkenes compared to alkanes?

  • Alkenes are unsaturated (contain double bonds)
  • More reactive than alkanes
  • Decolorize bromine water (test for alkenes)
  • Can form polymers by breaking double bonds