What is meant by the atom economy of a reaction?

It is a measure of the proportion of the total mass of the reactants that ends up as the desired product.

How is atom economy calculated from a balanced equation?

Divide the total relative formula mass of the desired product by the total relative formula mass of all the reactants, then multiply by 100.

Explain the difference between atom economy and percentage yield.

Atom economy is fixed by the balanced equation and shows how much of the reactant mass can ever become the desired product, while percentage yield measures how much of that possible product was actually obtained.

A process has a low atom economy. What happens to most of the mass of the reactants?

It leaves as by-products that are not wanted, and these must be separated and then sold or disposed of.

OCR GCSE Chemistry A J248

Chemical Reactions

Topic overview Writing formulae of elements and compounds Balanced equations, and deducing formulae from ions Ionic equations, and state symbols The mole and the Avogadro constant Conservation of mass, and changes of mass in open systems Stoichiometry, and calculating reacting masses Exothermic and endothermic reactions, and reaction profiles Activation energy, and bond energy calculations Oxidation and reduction, by oxygen and by electrons Acids, alkalis and neutralisation The ionic equation for neutralisation, and reactions of acids Dilute and concentrated, weak and strong The pH scale, and hydrogen ion concentration pH as a factor of ten, and measuring pH Products at the electrodes, and molten ionic compounds Electrolysis of aqueous solutions Inert and non-inert electrodes

Elements, Compounds and Mixtures

Topic overview Purity, and melting point data Relative formula mass and empirical formulae Formulations, and separating mixtures Paper and thin layer chromatography Interpreting chromatograms and Rf values Choosing a purification method Metals and non-metals in the Periodic Table Electron arrangement and position in the Periodic Table Ionic, covalent and metallic bonding compared Dot and cross diagrams, and the limits of models Reactions, electron arrangement and Mendeleev's table Carbon's four bonds, and the variety of organic compounds Diamond, graphite, fullerenes and graphene Bond strength, intermolecular forces and predicting state Bulk properties of ionic, molecular and giant structures Nanoparticles: size and surface area to volume Uses and risks of nanoparticulate materials

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Biological methods of metal extraction Rate against yield in industry, and reaction conditions The Haber process and fertiliser production Nitrogen, phosphorus and potassium in agriculture Life cycle assessment Recycling, and the decisions behind it Alloys, and the corrosion of metals Comparing glass, ceramics, polymers, composites and metals Functional groups and homologous series Predicting the products of organic reactions Addition polymerisation Condensation polymerisation, and making a polymer DNA and other natural polymers Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking Chemical cells and fuel cells The Earth's early atmosphere, and how oxygen developed The greenhouse effect, and evidence for climate change Effects of carbon dioxide and methane, and air pollutants Producing potable water

Monitoring and Controlling Chemical Reactions

Topic overview Concentration in mol/dm³, and titration Titration calculations, and the mass of a solute Molar gas volume and the volumes of gases Theoretical mass and percentage yield Atom economy, and choosing a reaction pathway Measuring the rate of a reaction, and rate graphs Factors affecting rate, and collision theory Surface area and rate Catalysts and how they work Reversible reactions and dynamic equilibrium Changing the conditions of an equilibrium Activation energy, and enzymes as catalysts

Particles

Topic overview The particle model and changes of state Limitations of the particle model How the atomic model changed, and the structure of the atom The size of atoms, and the subatomic particles Calculating protons, neutrons and electrons

Predicting and Identifying Reactions

Topic overview Groups 1, 7 and 0, and why they behave as they do Transition metals Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine Tests for aqueous cations and anions Flame tests, and identifying metal ions Identifying a species from test results Instrumental methods of analysis

Monitoring and Controlling Chemical Reactions

Atom economy, and choosing a reaction pathway

3 things to know
Paper 4

Overview

What atom economy is and how it is calculated, when it reaches 100%, why manufacturers want it high and how it differs from percentage yield, what happens to by-products, worked calculations for calcium oxide, iron, ammonia, hydrogen, oxygen and magnesium chloride, and choosing a reaction pathway by weighing atom economy, yield, rate, equilibrium position and useful by-products.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

When is atom economy 100%, why do manufacturers prefer a high atom economy, and how does atom economy differ from percentage yield?

Key term

Under what circumstances does a reaction have an atom economy of 100%?

Process

Give two reasons why a manufacturer prefers a process with a high atom economy.

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by the atom economy of a reaction?
Model answer
It is a measure of the proportion of the total mass of the reactants that ends up as the desired product.
2
How is atom economy calculated from a balanced equation?
Model answer
Divide the total relative formula mass of the desired product by the total relative formula mass of all the reactants, then multiply by 100.
3
Under what circumstances does a reaction have an atom economy of 100%?
Model answer
When there is only one product, so every atom in the reactants ends up in the substance that is wanted.
4
Give two reasons why a manufacturer prefers a process with a high atom economy.
Model answer
Less raw material is wasted as unwanted products, and there is less waste to separate and dispose of, so the process is cheaper and more sustainable.
5
Explain the difference between atom economy and percentage yield.
Model answer
Atom economy is fixed by the balanced equation and shows how much of the reactant mass can ever become the desired product, while percentage yield measures how much of that possible product was actually obtained.
6
A process has a low atom economy. What happens to most of the mass of the reactants?
Model answer
It leaves as by-products that are not wanted, and these must be separated and then sold or disposed of.

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Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

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