As you already know, atoms rearrange themselves into a new set of molecules during a chemical reaction. Usually, when we conduct a reaction we only care about one of the products. The other products are waste products. Atom economy tells us how many of the atoms in the reaction rearrange into the product we want. It shows us the desired product as a percentage of all the products formed.
- In this article you will learn about atom economy.
- We will consider how atom economy differs from percentage yield and why high atom economies are important in industry.
- Finally, you will learn how to calculate atom economy.
What is atom economy?
Atom economy shows how many of the atoms used in the reaction turned into the product we want.
By finding the atom economy of a reaction, we can discover how efficient it was. Efficient reactions have high atom economies because they produce less waste products. Inefficient reactions have low atom economies because they make more unwanted products.
Inefficient reactions produce waste products that are harmful to the environment.[2]
Chemical and waste reclamation centre by Ian Greig, CC BY-SA 2.0, via Wikimedia Commons
How is atom economy different from percentage yield?
You might remember that percentage yield also measures the efficiency of a reaction. It tells us how much of our reaction successfully turned into a product. What’s the difference?
Percentage yield is a value that we get experimentally. It measures the efficiency of a reaction based on the actual results from an experiment. However, atom economy is theoretical. It measures the efficiency of a reaction based on the balanced equation.
Why do industries want a high atom economy?
Efficient reactions have high atom economies. A reaction with a high atom economy is important in industry because it:
Uses fewer natural resources.
Produces less waste.
Is better for the environment.
Makes production cheaper.
Is more sustainable.
How to calculate atom economy
You can calculate the atom economy of a reaction by using the equation below:
We can also express the equation for the atom economy as shown below:
Did you notice the difference? In the first equation, we use the molecular masses of the products. However, we can also use the molecular masses of the reactants.
Does it matter? Remember, the Law of Conservation of Mass tells us that the number of atoms in the products and the reactants is the same. So, the sum of the products equals the sum of the reactants.
We can also calculate the atom economy by using the masses (instead of molecular mass) of the reactants and products. In this case, we can express the equation for the atom economy like this:
The atom economy for addition reactions is always 100 percent because they only produce the desired product. When there is only one product, the atom economy is 100 percent, since all the atoms turn into the desired product.
Jackie completed an experiment to produce Iron (Fe). The balanced equation for the experiment appears below. Calculate the atom economy for the product Iron (Fe).
Mr (Fe) = 56 x 2 = 112
(Jackie obtained 2 Fe atoms in the reaction)
Mr (products) = (56 x 2) + 3(12 + (16 x 2)) = 244
Atom Economy - Key takeaways
Atom economy shows how many of the atoms used in the reaction turned into the product we want.
Efficient reactions have high atom economies because they produce fewer waste products.
You can calculate the atom economy of a reaction by using this equation:Mr of Desired Product/ ∑ Mr of all the Products x 100
Percentage yield is different from atom economy. It measures the efficiency of a reaction based on the actual results from an experiment.
Atom economy is theoretical and measures the efficiency of a reaction based on the balanced equation.
- A reaction with a high atom economy is important in industry because it uses fewer natural resources, produces less waste, and is better for the environment. It is also cheaper to produce and more sustainable.
References
- Chemical and waste reclamation centre by Ian Greig, CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0), via Wikimedia Commons
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