Task Topic 2.3 is about considering the impact of chemistry on the planet and different methods for minimising this impact. Use the resources listed below to make detailed notes on the topic. Resources: These Slides Bangor AS Revision Guide Page 75 AS Textbook Page 122

The wider impacts of chemistry Topic 2.3

The energy problem Energy generation affects all aspects of life. As the Earth’s population rises, we have to continue to produce energy to meet the needs of all people We are currently heavily reliant on fossil fuels (finite resources) Some renewable resources are used (wind, solar, tidal, biomass, nuclear, geothermal etc.) but not in large enough quantities currently. Hydrogen is a potential renewable energy source but doesn’t exist naturally on Earth so is costly to produce.

The energy problem – fossil fuels All fossil fuels are technically solid stores of energy converted from sunlight. Formed from organic plant matter millions of years ago (see GCSE notes for actual formation process) The rate at which we use fossil fuels outstrips the natural production by over a factor of 100. This means they will run out at some point. CH2O CO2 + H2O C6H12O6 6CO2 + 6H2O Respiration Photosynthesis Respiration Photosynthesis

The energy problem – Carbon neutrality CO2 emissions are a huge problem associated with the burning of carbon based fuels Atmospheric concentrations of CO2 have increased from 300ppm to 400ppm in the past century Scientists have little doubt that this is leading to anthropogenic climate change (global warming) Carbon neutrality is achieved by offsetting the CO2 produced by planting trees that will absorb an equivalent amount. Some biomass is carbon neutral, this is due to the plant matter absorbing CO2 throughout it’s lifetime.

Nuclear power Nuclear fission has been used for over 50 years to generate electricity The processes is based on the famous equation E = MC2 Roughly 1% of mass in a reactor is converted to pure energy Huge drawbacks with the production of radioactive waste at the end of the process that is costly to treat and store. These products can last for millions of years. The process of setting up a nuclear Powerplant and maintaining its security is a labour intensive and very expensive process.

Nuclear fUsion A new and upcoming energy source. Works on the opposite principle of nuclear fission. Potential to create huge quantities of energy. Currently still not able to sustain fission and generate more electricity than is needed to run the process. Still developing, read up on stellarators and torus reactors if you’re interested.

Solar power Based on silicon or gallium arsenide semiconductor panels Can achieve efficiencies of 10% or more Use is rapidly growing In the UK we could hope to achieve outputs of 0.5kW/m2

Efficient use of energy To combat our use of energy and the potential of an energy crisis, one option is to look at making our energy use more efficient. E.g. the Carnot equation shows that combustion engines will never achieve efficiency greater than 37% We need to produce technology that is greener and uses less energy to complete a process.

Green chemistry – The principles Prevent waste Increase atom economy Use safer methods, chemicals and solvents Increase energy efficiency Use renewable raw materials (feedstocks) Use catalysis (vs. stochiometric reactions) Prevent pollution and accidents Design for biodegradation

Atom economy 𝐴𝑡𝑜𝑚 𝑒𝑐𝑜𝑛𝑜𝑚𝑦= 𝑀 𝑟 𝑜𝑓 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 𝑇𝑜𝑡𝑎𝑙 𝑀 𝑟 𝑜𝑓 𝑎𝑙𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 ×100 Essentially you are working out what percentage of the atomic mass of your desired products is actually contained within all products. Reactions that create only one product will have an atom economy of 100%

Use safer methods, chemicals and solvents Avoiding solvents that are harmful to the environment can be especially important, VOC’s can lead to photochemical smog. Carbon dioxide can be captured and liquefied, it is then useful as a solvent. Coffee and tea are decaffeinated using this process Adding hydrogen peroxide to polymer foams instead of sodium hypochlorite can prevent the production of sodium salts which need to be disposed of.

Use catalysts Oxidation is a vital chemical reaction. In chemistry we learn that acidified potassium dichromate is a useful reagent to oxidise. The Cr3+ ion is generated during this reaction. All chromium products are extremely harmful to the environment. Stoichiometry is the amounts of substances used in chemistry. In oxidation, one chromium product is produced for every oxidation reaction. Using platinum on carbon catalysts can eliminate the use of chromium by products with no harmful waste products.

Design for biodegradation PLA (poly lactic acid) is a polymer which is biodegradable, it is used in the production of bin bags. Producing more plastic bags using this material can mean less waste in landfill.