GCSE Chemistry revision

Atom economy

Yield and atom economy of chemical reactions (chemistry only)

AQA 4.3.3.2 Includes HT-only content

Your specification

AQA student objectives

Learning pathway

ALL 🎯

MOST 🎯🎯

SOME 🎯🎯🎯

Revision summary

Read on screen, then print for Cornell-style active revision.

Atom economy measures what percentage of the reactants are converted into useful, desired products rather than waste products.
It is particularly important in commercial chemical production, where reactions often produce multiple products but only one or two are actually useful.
The official equation for atom economy is: Atom Economy = (relative formula mass of desired product(s) / total relative formula mass of all reactants) × 100

1. What is Atom Economy? AQA

Atom economy measures what percentage of the reactants are converted into useful, desired products rather than waste products.
It is particularly important in commercial chemical production, where reactions often produce multiple products but only one or two are actually useful.
The official equation for atom economy is: Atom Economy = (relative formula mass of desired product(s) / total relative formula mass of all reactants) × 100

In the reaction of carbon monoxide and water to produce hydrogen, the desired product is hydrogen (H₂), which has an Mr of 2 × 1 = 2.
The reactants are carbon monoxide (Mr = 28) and water (Mr = 18), giving a total Mr of all reactants of 28 + 18 = 46.
The atom economy is therefore (2 / 46) × 100 = 4.35%, meaning only 4.35% of the reactants form the useful product, with 95.65% becoming waste.

2. Calculating Atom Economy: A Worked Example AQA

In the reaction of carbon monoxide and water to produce hydrogen, the desired product is hydrogen (H₂), which has an Mr of 2 × 1 = 2.
The reactants are carbon monoxide (Mr = 28) and water (Mr = 18), giving a total Mr of all reactants of 28 + 18 = 46.
The atom economy is therefore (2 / 46) × 100 = 4.35%, meaning only 4.35% of the reactants form the useful product, with 95.65% becoming waste.

A low atom economy, such as 4.35%, indicates that the vast majority of reactants are converted into waste rather than useful products.
A reaction with 100% atom economy, such as nitrogen reacting with hydrogen to form ammonia (N₂ + 3H₂ 2NH₃), produces only the desired product with no waste at all.
In general, a higher atom economy is more desirable as it means more of the reactants are being used efficiently to make the wanted product.

3. High vs Low Atom Economy AQA

A low atom economy, such as 4.35%, indicates that the vast majority of reactants are converted into waste rather than useful products.
A reaction with 100% atom economy, such as nitrogen reacting with hydrogen to form ammonia (N₂ + 3H₂ 2NH₃), produces only the desired product with no waste at all.
In general, a higher atom economy is more desirable as it means more of the reactants are being used efficiently to make the wanted product.

Raw materials are expensive, so if most reactants are converted into waste, the industrial process becomes less profitable.
Using large quantities of reactants to produce only small amounts of useful product is less sustainable and wastes finite resources.
Waste products can be costly to dispose of safely and may cause environmental damage if not managed properly.

4. Why Atom Economy Matters AQA

Raw materials are expensive, so if most reactants are converted into waste, the industrial process becomes less profitable.
Using large quantities of reactants to produce only small amounts of useful product is less sustainable and wastes finite resources.
Waste products can be costly to dispose of safely and may cause environmental damage if not managed properly.

One solution is to use a more efficient reaction that has a higher atom economy and produces less waste.
Another solution is to find a use for the waste products, converting them into useful byproducts that can be sold rather than disposed of.
Even selling by-products for a small profit is preferable to paying for waste disposal, improving both profitability and sustainability.

5. Solutions to Poor Atom Economy AQA

One solution is to use a more efficient reaction that has a higher atom economy and produces less waste.
Another solution is to find a use for the waste products, converting them into useful byproducts that can be sold rather than disposed of.
Even selling by-products for a small profit is preferable to paying for waste disposal, improving both profitability and sustainability.

Percentage yield is an important factor, as it measures how much of the desired product is actually obtained compared to the theoretical maximum.
The position of the equilibrium and the rate of reaction both affect how efficiently and quickly a useful product can be produced.
The cost of maintaining the correct reaction conditions, such as temperature and pressure, must also be considered when evaluating the overall profitability of an industrial process.

6. Other Factors Affecting Profitability AQA

Percentage yield is an important factor, as it measures how much of the desired product is actually obtained compared to the theoretical maximum.
The position of the equilibrium and the rate of reaction both affect how efficiently and quickly a useful product can be produced.
The cost of maintaining the correct reaction conditions, such as temperature and pressure, must also be considered when evaluating the overall profitability of an industrial process.