Cracking & Alkenes

• What is crude oil primarily composed of?

  A mixture of hydrocarbons
• How can different hydrocarbons in crude oil be separated?

  By the length of their carbon chains
• What process is used to separate hydrocarbons in crude oil?

  Fractional distillation
• Which hydrocarbons are the most flammable?

  The shortest hydrocarbons
• What is the characteristic of longer chain hydrocarbons?

  They are thick viscous liquids
• What is the process called that breaks down longer hydrocarbons into shorter ones?

  Cracking
• What type of reaction is cracking?

  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
• What are the two methods of cracking?

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

  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?

  They split into smaller hydrocarbons
• What is mixed with hydrocarbons in steam cracking?

  Steam
• What is produced when long chain alkanes are cracked?

  A shorter alkane and an alkene
• What is the product of cracking decane into ethene?

  Another alkane and ethene
• How do you determine the formula of the unknown alkane produced from decane and ethene?

  Subtract carbons and hydrogens of ethene from decane
• 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, alkanes have single bonds
• Why are alkenes more reactive than alkanes?

  They have a double bond
• What happens when bromine water is added to alkenes?

  It decolorizes from orange to colorless
• What is the significance of the bromine water test?

  It tests for the presence of alkenes
• What can alkenes be used to produce?

  Polymers and other chemicals
• What are the key features of alkenes compared to alkanes?

  • Alkenes have a double bond; alkanes have single bonds
  • Alkenes are unsaturated; alkanes are saturated
  • Alkenes are more reactive than alkanes
• What are the steps involved in the cracking process?

  1. Heat and vaporize long chain hydrocarbons
  2. For catalytic cracking, pass vapor over a catalyst
  3. For steam cracking, mix vapor with steam and heat
  4. Split long hydrocarbons into shorter ones
• What are the differences between catalytic cracking and steam cracking?

  • Catalytic cracking uses a catalyst (aluminium oxide)
  • Steam cracking uses steam and high temperatures
  • Both processes aim to produce shorter hydrocarbons