Chemical Sustainability

Percentage Yield

• Often in a chemical reaction, the amount of a product recovered is less than might have been expected from the amounts of the reactants used

Reasons for this include;

• The reaction may not have gone to completion because it is slow or reversible
• There may be competing side reactions which convert a proportion of the reactants into different products
• Some product may have been lost during purification

% Yield = actual moles of product/theoretical moles of product x 100

Atom economy

• A reaction may be intrinsically wasteful of there is more than one product and they are not all useful

Atom economy = Mr of desired product/sum of desired Mr of all products x 100

• Atom economy measures the proportion of the mass of material used up in the reaction that could ideally, be converted to useful product
• A reaction could have a high atom economy but be of little use in practice if there is a low yield due to competing side reactions or inefficient product recovery
• A reaction with high atom economy is preferable because it can make efficient use of resources and produce a low percentage of waste products

• Addition reactions have only one product, so atom economy is 100%
• Other reaction can have 100% atom economy only if all of the products are useful

Sustainability

Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs

Principles of chemical sustainability

• Using processes that reduce the use of hazardous chemicals and which involve using fewer chemicals
• Designing processes with a high atom economy and high % yield in order to minimise production of waste material
• Using renewable resources such as plant based substances
• Seeking alternative,r renewable energy sources to reduce our rate of consumption of fossil fuels
• Ensuring that waste products are non-toxic and can either be recycled or biodegraded to harmless substances in the environment

International Cooperation

• Kyoto protocol - agreement to reduce CO2 emissions to try to limit climate change
• Montreal protocol - agreement to ban the use of CFC's to reduce damage caused to the ozone layer