Cracking

• What is cracking in chemistry?

  Conversion of large hydrocarbons to smaller molecules
• Why does cracking require high temperatures?

  To split strong covalent bonds effectively
• What are the two main types of cracking?

  Thermal and catalytic cracking
• What is the economic reason for cracking hydrocarbons?

  Imbalance between abundance and demand of fractions
• Which petroleum fractions are in more demand?

  Shorter carbon chains like petrol and naphtha
• What happens to larger hydrocarbons during cracking?

  They are converted to shorter, more valuable hydrocarbons
• Why are the products of cracking more valuable?

  They are used for fuels and chemical production
• What is the temperature range for thermal cracking?

  400-900°C
• What pressure is required for thermal cracking?

  2000 kPa
• How long must molecules be exposed to high temperature in thermal cracking?

  Only for a second
• What types of bonds can be broken during thermal cracking?

  C-C and C-H bonds
• What is the general outcome of thermal cracking?

  Produces a high proportion of alkenes
• What is the general reaction for cracking high Mr alkanes?

  High Mr alkanes → smaller Mr alkenes + alkenes
• How does catalytic cracking differ from thermal cracking?

  Catalytic cracking uses lower temperatures and pressures
• What are the conditions required for catalytic cracking?

  Slight pressure, high temperature, zeolite catalyst
• What type of products does catalytic cracking produce?

  Branched chain alkanes and aromatics
• Why are branched chain alkanes added to motor fuels?

  They give fuels a higher octane number
• What is the effect of a higher octane number in fuels?

  Less knocking in the engine, better performance
• What is the role of ethene in chemical production?

  Used to make poly(ethene) and ethanol
• What is the significance of producing a high proportion of alkenes in thermal cracking?

  They are useful for manufacturing polymers
• Why is catalytic cracking considered more energy-efficient?

  It operates at lower temperatures and pressures
• How does the mechanism of catalytic cracking differ from thermal cracking?

  Catalytic cracking uses a catalyst and different conditions