Atom Economy

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Atom Economy
When we make a product in a chemical reaction, we often make other `by-products' as well.
The atom economy of a reaction is the percentage of the total mass of reactants that can, in
theory, be converted into the desired product. It can be calculated as follows:
% atom economy= mass of desired product/total mass of products x 100
The production of NaOH from NaCl the following reaction takes place:
2NaCl + 2H2O 2NaOH + H2 + Cl2
Assuming we start with 2 moles of NaCl and 2 moles of H2O, we will make 2 moles of NaOH,
and 1 mole of H2 and Cl2.
So % atom economy = (2 x 40) x 100 = 52.3 %
(2 x 40) + (1 x 2) + (1 x 71)
The remaining 47.7% of the mass is converted into less useful products and is hence wasted.
So the higher the atom economy, the less waste and the more efficient the product process
(assuming the reaction does actually go to completion).
All reactions which have only one product have an atom economy of 100%
Atom economy is an important consideration when considering how to make a particular
useful product.

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