Percentage Yield and Atom Economy

what is the percentage yield used for

• used to compare the actual yield obtained from a reaction with the maximum theoretical yield

• percentage yield of 100% would mean that no product has been lost or gained

what is the formula for percentage yield

yield from reaction

——-———————————- x 100

maximum theoretical yield

why might you not get the theoretical yield

• if the reaction is reversible, it might not go to completion

• some product could be lost when its seperted form the reaction mixture

• some if the reactants may react in a different ways to the expected reaction

what is atom economy

a measure of the amount of reactant that ends up in a useful product

what do scientist try to use when it comes to atom economy

• try to use a reaction pathway that have high atom economies

why is it good to use reaction pathways with high atom economies

• important for sustainable development

• as more products are made and less waste is produced

atom economy formula

relative formula mass of the desired product

————-————————————————————————— x 100

sum of the relative formula mass of all the products/reactants

how can ethanol be produced

• hydration

• fermentation

what is ethane reacted with during hydration

steam to form ethanol

ethane reaction

C2H4 + H2O → C2H5OH

what the atom economy for the hydration method

100%

what is the hydration of ethane reaction called

and addition reaction where all the reactant atoms end up in the desired product

how else can ethanol be produced apart from hydration

fermentation

how does the fermentation of ethanol work

ethanol is produced by the fermentation of glucose

fermenatation of ethanol

C6H12O6 → 2C2H5OH + 2CO2

what is the atom economy for the fermentation of ethanol

• much lower than hydration

• only half of the atoms in the reactant end up as the desired product

what are the important factors when choosing a reaction pathway

• the atom economy

• the cost of reactants

• the percentage yield

• the rate of reaction

• the equilibrium position

• the usefulness of by-products