11. atom economy & % yield Flashcards
formula for % yield
% yield = actual yield / theoretical yield x 100
why is actual yield always less than theoretical yield
some chemicals are lost
e.g. some is lost during transfer between containers or some solution gets left on filter paper
what can % yield tell us
how wasteful the process is
formula for atom economy
%atom economy = molecular mass of desired product/ sum of molecular mass of all products x100
what can atom economy tell us
the proportion of the reactant atoms that become part of the desired product
how can a reaction that has 100% yield still be wasteful?
atoms of reactants end up as byproducts rather than desired products
why is the atom economy for addition reactions always 100%
reactants combine to form a single produce
no atoms wasted
high atom economy has environmental and economic benefits
reaction with low atom economies less sustainable
low atom economy = lots of waste. costs money to separate desired product from waste products. costs to dispose of waste products safely so they don’t harm environment.
reactant chemicals = costly. waste of money if high proportion are useless products.
raw materials = limited supply. need to use efficiently so last as long as possible.
better for the environment if less waste is produced
in industry why are reaction conditions with low energy demand (low temperature and pressures) better
high energy demand = cost a lot to maintain.
low energy demand= cheaper to run and better for the environment.
what kind of raw materials are best for industry
renewable sources e.g. plants, enzymes better than non renewable sources e.g. crude oil, coal.
e.g. of a sustainable reaction
fermentation (renewable resources)
