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 Tip
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.
