3.3.2.2 Modification of alkanes by cracking

• What does cracking do?

  Converts ong chain fractions into more useful hydrocarbon fuels with shorter carbon chains, by breaking C-C bonds
• Name to 2 types of cracking?

  Thermal and Catalystic
• What does Thermal Cracking do?

  Produced a higher proportion/ percentage of alkenes, occurs in high pressure and temperature,
• What are the use of alkenes?

  To make polymers
• What is catalytic cracking?

  Produces a high proportion of branched alkanes and cyclic alkanes, makes more useful hydrocarbons, high temperature, slight pressure, catalyst is zeolite
• What is the name of the cataylst in catalytic cracking?

  Zeolite
• Use of catalyst?

  Lowers the activation energy, speeds up chemical reaction, increases rate of reaction, provides an alternative route
• What is reforming alkanes?

  Converts straight-chain alkanes into branched, cyclic alkanes and aromatic hydrocarbons, high temperature and pressure, catalyst platinum or rhodium
• Conditions needed for catalytic cracking?

  Temperature 500 degrees, pressure 1-2atm, zeolite catalyst
• Conditions needed for thermal cracking?

  Temperature 900 degrees, pressure 70atm, no catalyst
• Why is a lower temperature required for catalytic cracking than thermal cracking?

  Catalyst lowers the activation energy and temperature
• High Mr alkanes gives?

  Smaller Mr alkanes + alkenes + hydrogen
• Process on thermal cracking

  C-C bond chain splits, breaks homolytically (free radical), Mr high alkanes to smaller Mr alkanes, alkenes and H2, uses naphth fraction
• Why can steam be used in cracking?

  To increase its yield of alkenes
• Define a fraction

  Mixture of compounds with similar boiling points
• Define carbon-neutral

  No net emission of carbon dioxide