Atom Economy: A Measure of Reaction Efficiency
What is Atom Economy?
Atom economy
Atom economy is a measure of how efficiently the atoms in the reactants are used to form the desired product in a chemical reaction.
It is expressed as a percentage, where a higher atom economy indicates a more efficient reaction with less waste.
- The formula for atom economy is: $$
\text{Atom Economy} = \frac{\text{Molar Mass of Desired Product}}{\text{Sum of Molar Masses of All Products}} \times 100
$$ - This calculation considers the stoichiometry of the reaction and the masses of all products, not just the reactants.
- Unlike percentage yield, which measures how much of the desired product is obtained experimentally, atom economy is a theoretical measure based on the balanced chemical equation.
Atom economy focuses on the inherent efficiency of a reaction, making it a key metric in green chemistry for evaluating the environmental impact of chemical processes.
Calculating Atom Economy: A Step-by-Step Process
Let’s break down how to calculate atom economy using an example.
The Synthesis of Ethanol
Consider the hydration of ethene to produce ethanol:
$$
\text{C}_2\text{H}_4(g) + \text{H}_2\text{O}(g) \rightarrow \text{C}_2\text{H}_5\text{OH}(l)
$$
- Identify the desired product:
- In this reaction, ethanol ($\text{C}_2\text{H}_5\text{OH}$) is the desired product.
- Calculate the molar mass of the desired product:
- Molar mass of $\text{C}_2\text{H}_5\text{OH}$ = $2(12.01) + 6(1.01) + 16.00 = 46.08 \, \text{g mol}^{-1}$.
- Sum the molar masses of all products:
- Since ethanol is the only product, the sum of molar masses of all products = $46.08 \, \text{g mol}^{-1}$.
- Apply the formula: $$
\text{Atom Economy} = \frac{\text{46.08}}{\text{46.08}} \times 100 = 100\%
$$
This reaction has an atom economy of 100%, meaning all atoms in the reactants are incorporated into the desired product, with no waste.
HintReactions like the hydration of ethene are considered atom-efficient because they produce a single product without by-products.
Atom Economy and Green Chemistry
Why Does Atom Economy Matter?
- In the context of green chemistry, atom economy is a critical metric for designing sustainable chemical processes.
- High atom economy reduces waste, minimizes the need for disposal, and conserves resources.
- This makes it an essential consideration for industries aiming to reduce their environmental footprint.
