- Edexcel
Percentage yield and atom economy
I can perform calculations related to various aspects of industrial processes, and explain decision-making about the chosen reaction pathways in those processes.
- Edexcel
Percentage yield and atom economy
I can perform calculations related to various aspects of industrial processes, and explain decision-making about the chosen reaction pathways in those processes.
Lesson details
Key learning points
- In an ideal chemical reaction, all atoms in the reactants would end up in useful products, with no waste.
- The theoretical yield of a chemical reaction can be calculated from the reaction equation alone.
- The percentage yield shows how actual yield compares with theoretical yield.
- Atom economy is a measure of the efficiency with which a reaction uses its reactants.
- Many factors will be considered when choosing a reaction pathway.
Keywords
Theoretical yield - is the maximum calculated mass of product expected to form from a given mass of reactants
Actual yield - is the actual amount of product obtained from a chemical reaction
Percentage yield - is the actual yield (mass of product obtained) divided by the theoretical yield (maximum mass of product possible), as a percentage
Atom economy - is the percentage, by relative mass, of reactants that are converted into useful products
Useful product - is a chemical product that is desired or valuable
Common misconception
Pupils often confuse percentage yield with atom economy, thinking both measure the same efficiency aspect.
Clarify that percentage yield measures actual vs. theoretical product amount, while atom economy measures reactants' mass converted to desired product.
Equipment
None required.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Three beads are red and seven beads are green. What percentage of the beads are green?
Q2.Balance the following chemical equation:
CH₄ + O₂ → H₂O + CO₂
Q3.Calculate the relative formula mass (Mr) of calcium carbonate, CaCO₃.
Relative atomic masses (Ar): Ca = 40; C = 12; O = 16.
Q4.Which of the following statements about the equation below are correct?
2Mg + O₂ → 2MgO
Q5.When magnesium reacts with oxygen in the air to form magnesium oxide, magnesium is the limiting factor. There is more oxygen present than is needed, so we say that the oxygen is in .
Q6.Calculate the mass of 0.5 mol of magnesium. Give your answer to 2 s.f.
Relative atomic mass (Ar) of Mg = 24.
Assessment exit quiz
6 Questions
Q1.Match the following terms to the correct definitions.
Maximum calculated mass of product expected to form in a reaction.
Amount of product obtained from a chemical reaction.
Percentage of reactants converted into useful products.