The wider impact of chemistry 2.3

• Energy production is a major issue affecting all aspects of modern life
• Worldwide demands for energy are increasing greatly but our main source, fossil fuels, is being rapidly depleted
• Burning fossil fuels releases carbon dioxide into the atmosphere and oceans
• This has led to global warming, through an increase in the greenhouse effect
• Oceans are becoming more acidic with serious biological effects
• Alternative energy sources being sought

  • Hydrogen
  • Biomass
  • Solar energy
  • Nuclear fuel
• Hydrogen


  A clean fuel that, when consumed in a fuel cell, does not produce carbon dioxide, only water
• Hydrogen doesn't occur naturally on Earth, so it has to be produced
• The most common methods to produce hydrogen today are natural gas reforming and electrolysis
• Biomass energy


  Energy generated or produced by living, or once-living, organisms
• Burning plant-derived biomass releases carbon dioxide, but the carbon dioxide being generated is compensated for by that absorbed by the material during photosynthesis, making the whole process carbon neutral
• Solar power


  Capturing the energy from the Sun and converting it into electricity
• Solar power is a clean, renewable source of energy, but the cost of its collection, conversion and storage is still high
• Nuclear power produces no polluting gases, does not contribute to global warming and has very low fuel costs
• Public perception of the nuclear industry is negative because large scale accidents have been catastrophic
• Nuclear waste is radioactive and safe disposal is very difficult and expensive
• Green Chemistry aims to

  • Use renewable raw materials such as plant-based compounds wherever possible
  • Use as little energy as possible and get this from renewable sources rather than from fossil fuels
  • Use methods which have high atom economy, so there is little waste
  • Develop better catalysts, e.g. enzymes, to carry out reactions at lower temperatures and pressures
  • Make products that are biodegradable at the end of their useful lives
  • Avoid the use of toxic materials and ensure that there are no undesirable by-products
• Enzymes are biological catalysts that usually catalyse specific reactions and work best close to body temperature
• Benefits of enzymes


  • Lower temperatures and pressures can be used, saving energy and costs
  • They operate in mild conditions and do not harm fabrics or food, so are safe to use
  • They are biodegradable, so disposal is not a problem
  • They often allow reactions which form pure products to take place, with no side reactions, removing the need for complex separation techniques
• Problems with enzymes


  • Enzyme activity is affected by temperature (it increases until the protein denatures)
  • Enzyme activity is affected by pH (different enzymes have differing optimum pH levels)
  • Enzymes can be difficult to be removed from liquid products
• Burning fossil fuels produces CO2, which is a greenhouse gas and contributes to global warming
• Burning fossil fuels also produces oxides of sulphur and nitrogen, which are responsible for the formation of acid rain
• CFCs are responsible for making holes in the ozone layer, allowing UV rays from the sun to reach the earth's surface and cause skin cancer
• CO2 is not produced in the hydration of ethene, but fossil fuels are burned to achieve the temperature required for the process
• CO2 is produced in the process of fermentation, but plants have used CO2 in photosynthesis to produce the sugars