Atom Economy (OCR GCSE Chemistry A (Gateway))
Revision Note
Atom Economy
Along with the percentage yield, atom economy is used to analyse the efficiency of reactions
Most reactions produce more than one product and very often some of them are not useful
Atom economy studies the amount of reactants that get turned into useful products
It illustrates what percentage of the mass of reactants become useful products
It is used extensively in the analysis of systems and procedures in industries, in an effort to obtain sustainable development
It is also a very important analysis for economic reasons as companies prefer to use processes with higher atom economies
The higher the atom economy of a process then the more sustainable that process is
The equation for calculating atom economy is:
Worked Example
Hydrogen gas is obtained from methane in a process called steam-methane reforming.
The reaction is as follows:
CH4 (g) + H2O (g) → CO (g) + 3H2 (g)
Calculate the atom economy of this reaction.
Answer
Examiner Tips and Tricks
Unwanted by-products can sometimes be put to use, so although a low atom economy is a sign that a process is not green (sustainable) it doesn’t necessarily imply that the process is not economically viable.
The only way to improve the atom economy is to change the chemicals used. It cannot be improved by a more complete reaction or by reducing loss of reactants during the process, as is the case with percentage yield.
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