1. A single lesson - stand alone topic

5. It is rare for a reaction to convert 100% of the reactants entirely into the expected products. The reaction may not go to completion and there may be side reactions.

6. One approach is to work out the moles of starting material using n=m/m r If it is 1:1 then we would expect at most the same moles of product Use m=nM r (using Mr of product) to find maximum mass that could be obtained Then use % yield calculation as above

8. Calculate both the % yield and the atom economy

10. Calculating % Yield Calculate the moles of reactants used Calculate the expected maximum moles of product formed using a balanced equation Calculate the actual moles of product formed Find what % of the of the maximum moles were actually obtained.

11. Example 1 6.50g of bromoethane were heated under reflux with excess aqueous sodium hydroxide. After cooling and purification it was determined that only 0.562 g of ethanol was obtained. 1.Calculate the % yield of this reaction

13. Example 2 1000 kg of ethene was reacted with 750 kg of steam in the presence of an acid catalyst. It was later determined that 800 kg of ethanol had been obtained from the equilibrium mixture. The remainder was all un-reacted starting materials 1.Calculate the % yield of this reaction at equilibrium.

15. Addition vs Substitution It is not possible to accurately predict yields before we try the experiment out However we can always say that for an addition reaction that the atom economy will be exactly ………. % (great! ) For a substitution reaction the atom economy will be less than that (unless we are really trying to make both/all products – v unlikely) - not so good 

16. More questions you should probably try: P35-38 in the Clark Calculations book Problems 36,37 p 41 of the same book

17. I’ve just discovered a (made up!) molecule that upon heating gives a 100% yield of ethanol

18. a 100% yield of ethanol that’s great!!… The rest of the molecule just gets incinerated or flushed away

19. M r of waste = 278.4 M r of ethanol = 46.0 It may be a 100% yield reaction but the chemistry is no where near green enough for me!

20. M r of the waste product = 278.4 M r of ethanol = 46.0 It has a terrible atom economy - what is the percentage atom economy here?

21. Learn this it’s almost guaranteed to be tested!

23. Mini boards Without looking anything up write down the expression for atom economy

24. Work out the atom economy of the reaction of ethene with steam we considered earlier. What type of reaction is it? (common to alkenes)

25. Addition reactions will have a 100% atom economy. Nothing is left over. What can we say about substitution reactions?

26. Now carefully work through pages 120-121 in the orange book 1. In particular study the examples. Tackle SAQ 9 and 10