Atom Economy
Simple Explanation
Atom economy measures what percentage of the total mass of all reactants ends up in the desired product, rather than in unwanted by-products. It's a measure of how efficiently a reaction uses its atoms, not just how much product forms.
Why Do We Need It?
A reaction can have a great percentage yield but still waste a lot of material as by-products — atom economy captures a different, equally important kind of efficiency, especially important for reducing chemical waste.
Formula
Atom Economy
% atom economy = (desired product mass / total reactant mass) × 100
What percentage of the total reactant mass ends up in the desired product, rather than in by-products.
- desired product mass
- — the formula mass of the product you actually want
- total reactant mass
- — the combined formula mass of everything produced by the reaction, including by-products
When to use it: Whenever you need to measure how efficiently a reaction uses its atoms, especially when comparing different possible reaction routes.
Worked Example
Calculate atom economy
A reaction produces a desired product with a formula mass of 44, from total reactants with a combined formula mass of 80 (including by-products). What is the atom economy?
Why Does This Work?
Since the total mass of reactants must equal the total mass of all products (conservation of mass), the fraction that ends up specifically in the desired product — rather than in by-products — is exactly what atom economy measures.
Real-Life Example
Choosing a greener industrial process
Chemical companies often choose between two different reaction routes to the same product.
A route with higher atom economy wastes less raw material as by-products, making it both more environmentally friendly and usually cheaper to run at scale.
Practice
A reaction has a desired product mass of 36 and a total reactant mass of 90. What is the atom economy?
MediumCommon mistake
Confusing atom economy with percentage yield — percentage yield compares actual vs. theoretical amount of the SAME product; atom economy compares the desired product's mass to ALL the reactant mass, including unwanted by-products.
Quick Review
- % atom economy = (desired product mass / total reactant mass) × 100
- High atom economy means less mass wasted as by-products.
- Atom economy is different from percentage yield.