Atom Economy

Definition of Atom Economy

Atom economy is a measure of how efficiently atoms from the reactants are incorporated into the desired product of a chemical reaction. It is expressed as a percentage and shows the proportion of the total mass of reactants that ends up as useful product.

This concept is important in sustainable chemistry because it helps chemists design reactions that produce less waste and use resources more efficiently.

Calculating Atom Economy

To calculate atom economy, you need a balanced chemical equation. The calculation involves:

• Finding the relative formula mass (Mr) of the desired product.
• Finding the total Mr of all reactants.
• Using the formula:

This calculation tells you what percentage of the reactants' mass is converted into the useful product.

For instance, consider the reaction to make water:

Balanced equation: $2H_2 + O_2 \rightarrow 2H_2O$

- Mr of $H_2$ = 2, so for 2 moles: $2 \times 2 = 4$

- Mr of $O_2$ = 32

Total Mr of reactants = $4 + 32 = 36$

Mr of desired product $H_2O$ = 18, for 2 moles: $2 \times 18 = 36$

Atom economy = $\frac{36}{36} \times 100 = 100\%$

This means all atoms from the reactants are in the product, so the atom economy is 100%.

Importance of Atom Economy

Atom economy is important because it:

• Reduces waste: Reactions with high atom economy produce fewer unwanted by-products, meaning less chemical waste.
• Improves sustainability: Using more of the reactants efficiently conserves raw materials and reduces the environmental impact.
• Offers economic benefits: Less waste means lower disposal costs and better use of expensive raw materials, saving money for industries.
• Minimises environmental impact: Producing fewer by-products reduces pollution and the need for harmful chemical treatments.

Improving Atom Economy

Chemists can improve atom economy by:

• Choosing reactions with fewer by-products: Selecting synthetic routes that produce mainly the desired product.
• Using catalysts: Catalysts can make reactions more selective, increasing the amount of desired product formed.
• Using alternative synthetic routes: Designing new methods that avoid wasteful steps or side reactions.

For example, the production of biodiesel from vegetable oils uses a reaction with high atom economy compared to older methods that produced more waste.