Amount of Substance - Percentage Atom Economy (A-Level Chemistry)
Percentage Atom Economy
Atom Economy
% Atom Economy
A by-product is a secondary product made during the synthesis of another product.
The percentage atom economy is the way to measure how much of thereacting particles become the desired products in a reaction. The desired products exclude the by-products. The percentage atom economy can be calculated using the following equation:
% Atom Economy vs % Yield
The % yield of a reaction depends on the specific experiment – e.g. the same reaction might have 98% yield in an industrial plant, but a 30% yield in a school laboratory. % yield doesn’t consider side products.
The % atom economy is based on the equation. It is a measure of how much of the reactants (in terms of mass) is being converted into desired product. % atom economy does consider side products.
A reaction might have a low atom economy, which means that it produce little of the desired product in the equation, but still could have a 100% efficiency.
High Atom Economy in Industry Reactions
- A high % yield does not always mean the reaction is efficient. When a reaction has a high percentage yield it means that the actual yield of the product is very close to the theoretical yield of the product. However this would still be true if the majority of the reactants formed by-products instead of the desired product.
- The higher the % atom economy, the cheaper the process. The process of a reaction with a high percentage atom economy is less expensive because less time and machinery is needed to separate the desired product from the by-products and waste.
- The higher the % atom economy, the ‘greener’ the process. If the atom economy of a reaction is high, it means that it is more environmentally friendly because less waste is produced. These reactions are more sustainable because they use raw materials which are renewable and will never run out. This is one of the main reasons why the chemical industry encourages processes with high atom economies.
Calculations Involving % Atom Economy
In the AQA exam, you could be asked to calculate the percentage atom economy of a reaction from a balanced equation.
Practice Question: What is the percentage atom economy for the extraction of titanium, with the equation: TiO2 + 2Mg → Ti + 2MgO. (Ar values are as follows, Ti = 47.9, Mg = 24.3, O = 16)
1. Firstly write down the relative relative molecular masses (Mr) of all the reactants and the desired product mentioned in the question.
Mr of TiO2 = 47.9 + (16 x 2) = 79.9
Mr of 2Mg = 24.3 x 2 = 48.6
Ar of Ti = 47.9
2. Now calculate the percentage atom economy
% atom economy = ( 47.9 ÷ (79.9 + 48.6) ) x 100 = 37.3%
The amount of substance refers to the measurement of the number of entities (atoms, molecules, ions, etc.) in a chemical substance. It’s usually expressed in units of moles.
Understanding the amount of substance is crucial in A-Level Chemistry as it allows you to calculate the number of entities in a chemical reaction and predict the outcome. It’s also used to calculate the concentration of a solution, which is an important aspect of many chemical reactions.
The mole is the unit of measurement for the amount of substance. It’s defined as the number of entities (atoms, molecules, ions, etc.) in a substance that is equal to Avogadro’s number (6.022 x 10^23).
To calculate the number of moles in a substance, you need to divide the mass of the substance by its molar mass (the mass of one mole of the substance). The formula for this calculation is:
Number of moles = Mass of substance (in grams) / Molar mass (in grams/mol)
Percentage atom economy refers to the efficiency of a chemical reaction, calculated as the percentage of atoms that are incorporated into the desired product. In other words, it’s a measure of how much of the starting material is being used to make the desired product.
Percentage atom economy is important in A-Level Chemistry because it helps you evaluate the efficiency of a chemical reaction. A higher percentage atom economy indicates a more efficient reaction, as more of the starting material is being used to make the desired product. This is important in industrial chemical processes, where waste reduction and cost-effectiveness are key factors.
To calculate the percentage atom economy, you need to divide the total number of atoms in the desired product by the total number of atoms in the starting material and multiply the result by 100. The formula for this calculation is:
Percentage atom economy = (Total number of atoms in desired product / Total number of atoms in starting material) x 100
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