Topic 1 – Atom economy
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Atom economy
•
The atom economy of a chemical reaction is a measure of the amount of starting
materials that become useful products.
•
A high atom economy means that less waste is created and the reaction has a high
efficiency.
OR
How to calculate the atom economy for a reaction:
1) Calculate the molar mass of the products and reactants.
2) Multiply the molar masses by the coefficients in the balanced equation.
3) Identify the desired (useful) product(s).
4) Use the above equation to calculate the atom economy.
Example:
Calculate the atom economy for the following reaction:
2C2H5OCl + Ca(OH)2  2C2H4O + CaCl2 + 2H2O
1) Molar masses of reactants and products:
2) Multiply by coefficients:
3) Identify desired (useful) products:
4) Calculate atom economy:
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Topic 1 – Atom economy
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1) Calculate the atom economy for the following reaction for making hydrogen (H2) by
reacting coal with steam. Comment on the efficiency of the reaction.
C(s) + 2H2O(g)  CO2(g) + 2H2(g)
2) Titanium is manufactured by reacting titanium (IV) chloride with magnesium:TiCl4(s) + 2Mg(s)  Ti(s) + 2MgCl2(s)
Calculate the atom economy for this method of producing titanium. Comment of the
efficiency of the reaction.
3) Hydrazine, N2H4, was used as rocket fuel for the Apollo missions to the Moon. It can be
made by the reaction of ammonia with sodium chlorate, NaClO. The reaction is shown below:
2NH3(g) + NaClO(l)  N2H4(l) + NaCl(aq) + H2O(l)
Calculate the atom economy for this method of producing hydrazine. Comment of the
efficiency of the reaction.
4) Aluminium is extracted from purified aluminium oxide by electrolysis:
2Al2O3(s)  4Al(l) + 3O2(g)
a) Calculate the percentage yield for the case where 500.0g of aluminium are obtained from
1.00kg of aluminium oxide.
% 𝑦𝑖𝑒𝑙𝑑 =
𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
× 100
𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
b) Calculate the atom economy for the reaction. Comment of the efficiency of the reaction.
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