1. P ERCENTAGE Y IELD

2. D ID YOU KNOW ? The Haber process produces ammonia from gaseous nitrogen and hydrogen. Even though it is done under the best possible temperature and pressure, in the presence of a catalyst, the process only yields about 15% of product. However, even at this level of efficiency, it is still economical to produce ammonia this way!

3. P ERCENTAGE YIELD Equations used to represent chemical reactions show the maximum amount of substance that can be produced in the reaction. For example, the following reaction shows that 2 mol of H2 and 1 mol of O2 can produce 2 mol of H2O. 2H 2 + O 2  2H 2 O It is impossible to produce more than 2 mol H2O from 2 mol of H2 and 1 mol of O2. It is also impossible to produce 2 mol H2O from less than 2 mol of H2 and 1 mol of O2. It is possible, however, to produce less product than expected. As in gambling, you will probably lose, you may break even, but you can’t win (get more out than you put in).

4. V OCABULARY The theoretical yield is the maximum amount of product that could be formed from given amounts of reactants. In contrast, the amount of product that actually forms when the reaction is carried out in the laboratory is called the actual yield. The actual yield is often less than the theoretical yield. This can be caused by experimental errors such as lost product, incomplete reaction, contamination, and inadequate reaction conditions. The percentage yield is the ratio of the actual yield to the theoretical yield expressed as a percentage. The percentage yield measures the efficiency of the reaction.

5. E XAMPLE An organic chemist reacts 10 g of CH4 with excess Cl2. She obtained 10 g of CH3Cl and some H2. a) What is the theoretical yield? b) What is her percentage yield? So, the theoretical yield is 31.47 g of CH3Cl. So, the percentage yield is 31.78%

6. C HECK Y OUR U NDERSTANDING 36 g of ethyl ethanoate (CH3CO2C2H5) are obtained from 23 g of ethanol (C2H5OH) using the following equation: C 2 H 5 OH + CH 3 CO 2 H  CH 3 CO 2 C 2 H 5 + H 2 O What is the % yield?

7. C ANADIANS I N C HEMISTRY He extended his research into photochemistry and chemical kinetics after joining the National Research Council (NRC) as Director of the Division of Chemistry in 1939. He played a leading role in British-Canadian collaboration in atomic energy, which led to the construction of the Chalk River reactor, the first to be built outside the USA. In 1950 Steacie became Vice-President of the NRC, then president two years later. He is perhaps best known as an administrator and statesman of science for Canada, since he was very instrumental in building up university research in Canada and was the architect of enduring programs to support industrial innovation. Various awards have been established in his honour, including the Steacie Memorial Prize, which recognizes the achievements of young Canadian scientists. Source: http://www.science.ca/ Edgar William Richard Steacie is a Canadian physical chemist. He pioneered research into chemical reactions and helped found university research programs in Canada. Steacie was educated at McGill University in the 1920s where he began his teaching career as well as conducting ground-breaking research in free radical chemistry.