Green Chemistry This lesson we will... Wednesday 23rd March Green Chemistry This lesson we will... Describe ways in which the processes in the chemical industry are being reinvented to make them more sustainable (‘greener’)

What do these terms mean? Sustainability Carbon footprint Carbon neutral

Sustainability Using resources effectively today without compromising their use in the future.

Carbon footprint A carbon footprint is a measure of the impact that human activities have on the production of carbon dioxide.

Carbon neutral A carbon neutral fuel offsets the carbon dioxide produced through combustion by absorbing carbon dioxide whilst it is growing.

Global Warming and Climate Change

Carbon Neutral Fuels

Waste Management and Sustainability

ALL OF THESE WILL REDUCE COSTS Developing processes to become more sustainable – Why? Reduce waste Lower activation energy Find an alternative mechanism / pathway for a reaction to take place Better atom economy Reduce carbon footprint ALL OF THESE WILL REDUCE COSTS

1. Which factors need to be taken into account when evaluating the ‘sustainability’ of a particular process? 2. Describe the concept of a carbon neutral fuel such as hydrogen or bio-ethanol. Why is it so difficult for a fuel to actually be ‘carbon-neutral’? 3. Explain why the development of new catalysts and alternative reaction pathways is a priority area for chemical research today. 4. Explain the principles of Global warming, and the difference between anthropogenic and natural climate change.

EVALUATING SUSTAINABILITY – FACTORS TO CONSIDER TEMPERATURE AND PRESSURE REQUIRED ATOM ECONOMY TOXIC/HARMFUL WASTE PRODUCTS EASE OF SEPARATING PRODUCTS AVAILABILITY OF REACTANTS YIELD OF REACTION CATALYST USED? HOW OFTEN DOES IT NEED TO BE REPLACED?

The Ozone Layer and CFCs Tuesday 29th March The Ozone Layer and CFCs This lesson we will… Describe and explain the effect of CFCs on the ozone layer

What determines if a gas acts as a greenhouse gas? Which of these gases will absorb IR radiation? Greenhouse gases absorb infrared radiation and re-emit it as heat. N Ξ N O = C = O O = O Molecules with polar bonds absorb IR

.O. .O. .O. 2 .O. O2 O2 O3 O3 O2 O3 O2 The “ozone-oxygen cycle” UV UV Natural cycle that maintains the concentration of O3 at 0.2-0.4ppm in the stratosphere O3 .O. O2 UV

What is the point of ozone? Ozone absorbs UV light which can cause severe damage to DNA of skin cells if it reaches us, causing skin cancer. It also causes sunburn. The “hole” in the ozone layer is a region in the southern hemisphere above Antarctica where the concentration of ozone in the stratosphere is much lower than it should be. (There is not a big hole!)

NO NO2 NOx NO + O3 NO2 + O2 NO2 + O3 NO3 + O2 Depletion of Ozone Aeroplanes emit nitrogen oxides which deplete the concentration of ozone: NO NO2 NOx NO + O3 NO2 + O2 NO2 + O3 NO3 + O2

Are CFCs greenhouse gases? CFC’s are chloro-fluoro-carbons, for example 1,1,2,-trichloro-1,2,2-trifluoroethane. Are CFCs greenhouse gases? Developed as refrigerants and for use in aerosols as they are very un-reactive. This means that when CFC molecules are released into the atmosphere they do not react with anything so don’t degrade. They are able to diffuse up to the stratosphere where the carbon-halogen bonds are homolytically cleaved by UV light causing the production of halide radicals.

Cl. + O3 g ClO. + O2 ClO. + O3 g 2O2 + Cl. Or ClO. + .O. g O2 + Cl. These halide radicals then react with ozone molecules destroying it. The product from the reaction (ClO.) also reacts with further ozone molecules or oxygen radicals. This cycle can continue for years, continually destroying ozone. Cl. + O3 g ClO. + O2 ClO. + O3 g 2O2 + Cl. Or ClO. + .O. g O2 + Cl.