Chemrevise

• What is the first step in refining crude oil?

  Oil is pre-heated
• What happens to the fractions during fractional distillation?

  They condense at different heights
• How does the temperature change in the fractional distillation column?

  The temperature decreases upwards
• Where do small molecules condense in the distillation column?

  At the top at lower temperatures
• Where do big molecules condense in the distillation column?

  At the bottom at higher temperatures
• What is the process of fractional distillation in refining crude oil?

  • Oil is pre-heated and passed into a column.
  • Fractions condense at different heights based on boiling points.
  • Temperature decreases upwards in the column.
  • Separation depends on the size of molecules and their boiling points.
• What is the purpose of a vacuum distillation unit?

  To distill heavy residues under a vacuum
• How does lowering pressure affect boiling points?

  It lowers the boiling point of liquids
• What is petroleum primarily composed of?

  Alkane hydrocarbons
• What is a petroleum fraction?

  A mixture of hydrocarbons with similar chain length
• What is the boiling point of petrol/gasoline?

  20°C
• What is the boiling point of kerosene (jet fuel)?

  180°C
• What is the purpose of fractional distillation in the laboratory?

  To separate liquids with similar boiling points
• What is the role of the thermometer in fractional distillation?

  It should be at or below the boiling point
• What happens to vapours with higher boiling points during distillation?

  They condense back into the flask
• What is the main product of thermal cracking?

  Mostly alkenes
• Why is cracking economically important?

  To meet demand for shorter hydrocarbons
• What is cracking in the context of hydrocarbons?

  Conversion of large hydrocarbons to smaller ones
• What type of bonds are broken during cracking?

  C-C bonds
• What are the conditions for thermal cracking?

  High pressure and high temperature
• What is the main advantage of catalytic cracking over thermal cracking?

  It uses lower temperatures and pressures
• What is produced during complete combustion of alkanes?

  CO2 and H2O
• What is the result of incomplete combustion?

  Produces CO and/or C
• What is a consequence of carbon soot from incomplete combustion?

  Global dimming
• How can SO2 be removed from waste gases?

  By flue gas desulfurisation
• What is the reaction that occurs during flue gas desulfurisation?

  SO2 reacts with calcium oxide
• What is formed when calcium oxide reacts with SO2?

  Calcium sulfite
• What is the environmental consequence of nitrogen oxides?

  They form acid rain
• What do catalytic converters remove from exhaust gases?

  CO, NOx, and unburned hydrocarbons
• What is the overall reaction for CO and NO in catalytic converters?

  2 CO + 2 NO → 2 CO2 + N2
• What are the main greenhouse gases?

  CO2, CH4, and H2O
• What is the mechanism of the greenhouse effect?

  CO2 absorbs infrared radiation
• What is the overall reaction for the formation of chloromethane?

  CH4 + Cl2 → CH3Cl + HCl
• What is a free radical?

  A reactive species with an unpaired electron
• What is the first step in the free radical substitution mechanism?

  Initiation with UV light
• What happens during the propagation step of free radical substitution?

  A free radical reacts with a molecule
• What occurs during the termination step of free radical substitution?

  Two free radicals collide
• What happens if excess Cl2 is present during substitution reactions?

  Further substitution can occur
• What is the overall reaction for the formation of CCl4 from CH4?

  CH4 + 4 Cl2 → CCl4 + 4 HCl
• What is the importance of placing the free radical dot on the correct carbon?

  It ensures accurate substitution on the carbon