A Level Chemistry OCR Practice Exam

How is atom economy calculated?

1. Molecular mass of product divided by reactant mass

2. Molecular mass of the desired product times 100 over total molecular mass of all products

3. Sum of molecular masses of products divided by atom count

4. Mass of reactants divided by mass of products

The correct answer is: Molecular mass of the desired product times 100 over total molecular mass of all products

Atom economy is a measure of the efficiency of a chemical reaction in terms of how well it utilizes the starting materials (reactants) to produce the desired product. It is calculated by taking the molecular mass of the desired product, multiplying it by 100, and dividing this by the total molecular mass of all products formed in the reaction. This calculation is important because it provides insight into the sustainability and environmental impact of a chemical process. A higher atom economy implies that a greater proportion of reactants has been converted into the desired product, minimizing waste and the generation of by-products. In contrast, the other options do not accurately describe the concept of atom economy. For example, the first option deals with reactant masses rather than focusing on the efficient conversion to products. The third option confuses total molecular masses and atom counts, which are not relevant in this context. Lastly, the fourth option refers to mass ratios, which do not provide the necessary information about how effectively reactants have been transformed into useful products.