Atom Economy
Learning outcomes

Atom economy is derived from the principles of green
chemistry.

Atom economy is a measure of the proportion of reactants
that become useful products.
Mass of desired product(s)

% atom economy =
x 100
Total mass of reactants
What is
green chemistry?

The sustainable design of chemical products and
chemical processes.

It minimises the use and generation of chemical
substances that are hazardous to human health or the
environment.
Green chemistry
principles

Better to prevent waste than to treat it or clean it up.

Chemical processes should aim to incorporate all reactants
in the final product.

Chemical processes should aim to use and generate
substances with minimal toxicity to human health and the
environment.
The green chemical
industry
 Modern chemists design reactions with the highest possible
atom economy in order to minimise environmental impact.
 Chemists achieve this by reducing raw material and energy
consumption.
Percentage yield
Actual yield
% yield =
x 100
Theoretical yield

Historical method for evaluating reaction efficiency.

Measures the proportion of the desired product
obtained compared to the theoretical maximum.

Gives no indication of the quantity of waste produced.
Atom economy
 In an ideal reaction, all reactant atoms end up within
the useful product molecule. No waste is produced!
 Inefficient, wasteful reactions have low atom economy.
 Efficient processes have high atom economy and are
important for sustainable development. They conserve
natural resources and create less waste.
Atom economy
Mass of desired product(s)
% atom economy =
x 100
Total mass of reactants
 A measure of the proportion of reactant included in the
final useful product.
 A reaction may have a high percentage yield but a low
percentage atom economy, or vice versa.
High atom economy
All reactant atoms included in the desired
product.
Low atom economy
Some reactant atoms not included in the desired
product.
Example 1
What is the percentage atom economy for the following reaction
for making hydrogen by reacting coal with steam?
C(s)
+
2H2O(g) → CO2(g)
+ 2H2(g)
12 g
2(2 + 16) g
[12 + (2 × 16)] g
12 g
36 g
44 g
2(2 × 1) g
4g
Total mass of reactants
Mass of desired product
= 12 + 36 = 48 g
=4g
Example 1 (contd)
% atom economy = mass of desired product × 100
total mass of reactants
4 × 100
=
48
= 8.3%
This reaction route has a very low atom economy and is
an inefficient method of producing hydrogen.
Example 2
Calculate the percentage atom economy for the reaction
below.
CH3
H3C
C
acid
H3C
CH CH2
CH3
C6H12
Total mass of reactants
= [(6 × 12) + (12 × 1)]
= 84 g
CH3
C
H3C
C
CH3
C6H12
Mass of desired product
= [(6 × 12) + (12 × 1)]
= 84 g
Example 2 (contd)
% atom economy = mass of desired product × 100
total mass of reactants
=
84 × 100
84
= 100%
This reaction route has a very high atom economy as all
reactant atoms are incorporated into the desired product.
Example 3
Hydrazine (N2H4) is used for rocket fuel. Calculate the atom
economy for hydrazine production.
2NH3
+
NaOCl
N2H4
NH3
2 mol
NaOCl
1 mol
N2H4
1 mol
NaCl
1 mol
H2O
1 mol
34 g
74.5 g
32 g
58 g
18 g
+
NaCl
Total mass of reactants
Mass of desired product
= 34 + 74.5 = 108.5 g
= 32 g
+
H2O
Example 3 (contd)
% atom economy = mass of desired product × 100
total mass of reactants
=
32 × 100
108.5
= 30%
This reaction route has an atom economy of 30%. The
remaining 70% is waste product (NaCl and H2O).
Catalysts

Have a crucial role in improving atom economy.

Allow the development of new reactions requiring fewer
starting materials and producing fewer waste products.

Can be recovered and re-used.

Allow reactions to run at lower temperatures, cutting energy
requirements.