Fuels & earth science

• What are hydrocarbons?

  Compounds that contain carbon and hydrogen only
• How can crude oil be described?

  • A complex mixture of hydrocarbons
  • Contains molecules with carbon atoms in chains or rings
  • An important source of useful substances (fuels and feedstock for the petrochemical industry)
  • A finite resource
• What is the process of fractional distillation used for in crude oil processing?

  • Separates crude oil into simpler, more useful mixtures
  • Different hydrocarbons have different boiling points
  • Crude oil is heated in a fractionating column
  • Vaporized oil rises and condenses at different temperatures
  • Various fractions are tapped off at different levels
• What is the boiling point trend for hydrocarbons in crude oil?

  Longer chain hydrocarbons have higher boiling points
• What are the uses of the different fractions obtained from crude oil?

  Gases for domestic heating and cooking, petrol for cars, kerosene for aircraft, diesel oil for cars and trains, fuel oil for ships and power stations, bitumen for roads and roofs
• How do hydrocarbons in different fractions differ from each other?

  • Number of carbon and hydrogen atoms
  • Boiling points
  • Ease of ignition
  • Viscosity
  • Mostly members of the alkane homologous series
• What happens to the viscosity of hydrocarbons as the size of their molecules increases?


  Longer molecules are more viscous
• How does the boiling point of hydrocarbons relate to their molecular size?


  Shorter molecules have lower boiling points
• What is a homologous series?


  A series of compounds with the same general formula, differing by CH₂, showing gradual variation in physical properties
• What are the characteristics of a homologous series?


  • Same general formula
  • Differ by CH₂ in molecular formulae
  • Gradual variation in physical properties (e.g., boiling points)
  • Similar chemical properties
• What are the products of the complete combustion of hydrocarbon fuels?

  Carbon dioxide (CO₂) and water (H₂O)
• What type of reaction is the complete combustion of hydrocarbons?


  Exothermic reaction
• What occurs during incomplete combustion of hydrocarbons?


  Produces carbon and carbon monoxide due to insufficient oxygen
• How does carbon monoxide behave as a toxic gas?


  It prevents red blood cells from carrying oxygen, which can lead to death
• What problems are caused by incomplete combustion producing carbon monoxide and soot?


  • Carbon monoxide causes health problems
  • Soot causes global dimming
• How do impurities in hydrocarbon fuels lead to the production of sulfur dioxide?


  Sulfur in fuels reacts with oxygen during combustion to form sulfur dioxide
• What are some problems associated with acid rain caused by sulfur dioxide?


  • Damages buildings and statues (made of limestone)
  • Reduces growth of or kills trees and crops
  • Lowers pH of water in lakes, killing fish
• What pollutants are produced when fuels are burned in engines at high temperatures?


  Oxides of nitrogen
• How do nitrogen and oxygen react in engines to produce pollutants?


  • Nitrogen and oxygen combine to produce nitrogen monoxide
  • Nitrogen monoxide combines with oxygen to form nitrogen dioxide
  • Both nitrogen monoxide and nitrogen dioxide are pollutants
• What are the advantages and disadvantages of using hydrogen as a fuel in cars compared to petrol?

  Advantages:

  • Hydrogen is a renewable resource
  • Only produces water, no CO₂ emissions

  
  

  Disadvantages:

  • Expensive
  • Difficult to transport and store
  • Can be explosive
• What are petrol, kerosene, and diesel oil classified as?

  • Non-renewable fossil fuels obtained from crude oil
  • Methane is a non-renewable fossil fuel found in natural gas
• What is the process of cracking in hydrocarbons?

  • Breaking down larger, saturated hydrocarbon molecules into smaller, more useful ones
  • Involves heating hydrocarbons to vaporize them
  • Products include alkanes and unsaturated hydrocarbons (alkenes)
• What is the general formula for alkenes?


  C_nH_2n
• What are the first two alkenes?

  Ethene and propene
• Why is cracking necessary in the production of hydrocarbons?


  Demand for smaller chained alkanes is much greater than for longer chained alkanes
• Why are shorter chained hydrocarbons more useful as fuels?

  They ignite more easily
• What gases produced by volcanic activity formed the Earth's early atmosphere?


  Gases released by volcanic activity
• How did volcanic activity contribute to the formation of the early atmosphere?


  It released gases that formed the early atmosphere
• What was the composition of the early atmosphere similar to?


  It may have been like the atmospheres of Mars and Venus today
• What was the primary gas in the early atmosphere?

  Carbon dioxide (CO2)
• What other gases were produced by volcanoes during the formation of the early atmosphere?


  Nitrogen, methane (CH4), and ammonia (NH3)
• What was the state of oxygen in the Earth's early atmosphere?


  There was little or no oxygen
• What was the amount of CO2 in the Earth's early atmosphere?


  A large amount of CO2
• What other components were present in the early atmosphere?

  Water vapor and small amounts of other gases
• How did oceans form from water vapor in the early atmosphere?

  Water vapor condensed to form oceans
• What is the chemical change that occurs when water vapor condenses?


  H2O (g) -> H2O (l)
• How did the amount of CO2 in the atmosphere decrease as oceans formed?


  CO2 dissolved in water and carbonates were precipitated
• What process produced oxygen in the atmosphere from primitive plants?

  Photosynthesis
• What is the equation for photosynthesis?


  6CO2 + 6H2O -> C6H12O6 + 6O2
• When did algae first produce oxygen?

  About 2.7 billion years ago