CC16 Fuels

• Natural gas and crude oil are natural resources made from the remains of microscopic marine plants and animals that died millions of years ago.
• Crude oil and natural gas are finite resources because they are not being made any more (or are being made extremely slowly), which limits the amounts available to us.
• Crude oil is a mixture of hydrocarbons.
• A hydrocarbon is a compound that contains the elements carbon and hydrogen ONLY.
• Carbon atoms can each form 4 covalent bonds, so the carbon atoms in hydrocarbon molecules are able to join together in different ways, forming chains and rings.
• • Different hydrocarbons have different boiling points so crude oil is separated by fractional distillation.
• Crude oil is a mixture of hydrocarbon molecules and the different hydrocarbons must be separated out into simpler, more useful mixtures.
• • Crude oil isn’t runny enough or ignited easily enough for it to be useful as a fuel.
• Crude oil is an important source of useful substances, including:

  • Fuel for vehicles (petrol and diesel oil), large ships, power stations and aircraft (kerosene). 
  • Methane, domestic heating.
  • raw materials for the petrochemical industry. Petrochemicals are substances made from crude oil, such as poly(ethene) and other polymers.
• Short carbon chains, low boiling points, runny (not viscous), easily ignited and light in colour.
• Long carbon chains, high boiling points, viscous, not easily ignited and darker in colour.
• fractional distillation of crude oil

  
• Each fraction is a mixture of hydrocarbons which have similar numbers of carbon and hydrogen atoms and similar boiling points.

  Different fractions have different uses because they have different properties.
• A fraction is not a chemically pure substance but is a mixture of similar
• alkanes = saturated, single bonds
• An homologous series is a series of compounds that have these features in common:

  the molecular formula of neighbouring compounds differ by CH2 

  they have the same general formula

  they show a gradual variation in physical properties, such as their boiling points

  they have similar chemical properties.
• CnH2n+2 = alkane formula
• alkenes = unsaturated, double bonds
• CnH2n = alkene formula
• Complete combustion of a hydrocarbon occurs in a plentiful supply of oxygen and:

  • only water and carbon dioxide are produced. 

  energy is given out.
• Incomplete combustion happens in a limited supply of air and: water is produced.

  energy is given out (but less than with complete combustion).

  carbon monoxide (CO) and carbon particles (soot) are produced
• Carbon monoxide is a toxic gas. It combines with haemoglobin in red blood cells, preventing oxygen combining. This reduces the amount of oxygen carried in the bloodstream. leading to drowsiness, unconsciousness and can even cause death
• • Soot can block the pipes carrying away waste gases from an appliance and can blacken buildings. It can cause breathing problems if it collects in the lungs.
• • ACID RAIN is rain that is more acidic than normal and has a pH lower than 5.2.
  • Hydrocarbon fuels (such as petrol and diesel oil) may contain sulfur compounds as impurities.
  • The hydrocarbon is burnt and the sulfur reacts with oxygen to form sulfur dioxide gas.

  S(s) + O2(g)🡪 SO2(g)

  • This dissolves in rain water (clouds) to form acid rain which causes damage to buildings, plants and can kill fish in lakes.
• • Catalytic converters in cars convert most of the NOx in exhaust gases to harmless nitrogen.
  • The temperature’s high enough for nitrogen and oxygen in the air inside the engine to react together to produce various oxides of nitrogen. 
  • Nitrogen dioxide, NO2, forms dilute nitric acid when it dissolves, which falls as acid rain.
• problems with acid rain :      Acid rain makes soils acidic – crops don’t grow well when the soil is too acidic. Acid rain makes rivers and lakes acidic. Acid rain increases the rate of corrosion of metals.
• Reducing environmental damage

  • Adding calcium carbonate or calcium hydroxide (alkali) to fields and lakes to neutralise excess acid from acid rain
  • Removing sulphur from petrol, diesel oil and fuel oil at the refinery before selling it.
  • Preventing sulfur dioxide gas leaving power station chimneys by spraying calcium carbonate through the acidic gas emissions to neutralise them (flue gas desulfurisation)
• Alternative fuels - Hydrogen

  The hydrogen fuel could be dangerous.  hydrogen is easily ignited and its combustion releases large amounts of energy.

  gas at room temperature which makes it difficult to store in large amounts. the combustion of hydrogen produces water but no carbon dioxide.
• Fractions with small molecules, like petrol, are in much higher demand than the fractions with large molecules (bitumen and fuel oil) and yet the larger molecules are in more supply.
• Cracking:

  • Breaking down large hydrocarbon molecules into smaller more useful ones, so that we can supply enough petrol for our needs.
• To prevent ‘suck back’ during cracking you should remove the delivery tube from the water before you stop heating with the Bunsen burner (otherwise cold water could come up the tube and into the hot boiling tube, shattering the glass)
• • In cracking, crude oil fractions are heated to evaporated them and these vapours are passed over a catalyst containing aluminium oxide and heated to about 650OC. This speeds up reactions to break down some of the carbon–carbon bonds in the larger hydrocarbons. 
  • This is a thermal decomposition reaction.
• There are exactly the same numbers of carbon and hydrogen atoms before and after cracking!