Cracking

• What is the process called that converts long chain hydrocarbons into shorter chain hydrocarbons?

  Cracking
• What is meant by cracking in the context of hydrocarbons?

  Cracking is the process of breaking down long chain alkanes to produce smaller, more useful molecules.
• What is the general formula for alkanes?

  C$n$H$2n +$$2$
• What type of bonds do alkanes have between carbon atoms?


  Alkanes have single covalent bonds between carbon atoms.
• Why are long chain hydrocarbons not considered good fuels?

  Long chain hydrocarbons are not very flammable.
• What are the two methods of carrying out cracking?

  Catalytic cracking and steam cracking.
• What conditions are used in catalytic cracking?

  High temperature and a catalyst.
• What is the name of the alkene produced from cracking?

  Ethene
• What type of bond do alkenes have between carbon atoms?

  Alkenes have a double covalent bond between two carbon atoms.
• Why are alkenes considered more reactive than alkanes?

  Alkenes are more reactive due to the presence of a double bond.
• How do we test for the presence of alkenes?

  By shaking the alkene with bromine water, which turns colorless.
• What color does bromine water turn when it reacts with an alkene?

  Colorless
• What is the importance of stating that bromine water turns colorless in the exam?

  It is important to specify that it turns colorless, not clear, as that is incorrect terminology.
• How do you balance a chemical equation for cracking?

  You ensure that the number of carbon and hydrogen atoms is the same on both sides of the equation.
• In a cracking equation, if the left side has 25 carbon atoms and 52 hydrogen atoms, and the right side has 20 carbon atoms and 42 hydrogen atoms, how many carbon and hydrogen atoms are in the second product molecule?

  The second product molecule must have 5 carbon atoms and 10 hydrogen atoms.
• If the left side of a cracking equation has 40 carbon atoms and 82 hydrogen atoms, and the right side has 7 carbon atoms and 14 hydrogen atoms, how many carbon and hydrogen atoms are in the first product molecule?

  The first product molecule must have 33 carbon atoms and 68 hydrogen atoms.
• What are the uses of alkenes?

  • Used to make polymers
  • Serve as starting materials for other useful chemicals
• What are the key features of alkanes and alkenes?

  Alkanes:

  • General formula: C$n$H$2n +$$2$
  • Single covalent bonds

  
  

  Alkenes:

  • Double covalent bond between carbon atoms
  • More reactive than alkanes