Limiting reactants
I can identify a reactant as being in excess or the limiting reactant and use that information to calculate a theoretical yield.
Limiting reactants
I can identify a reactant as being in excess or the limiting reactant and use that information to calculate a theoretical yield.
Lesson details
Key learning points
- In a chemical reaction, the atoms in reactants are rearranged and are the same atoms that are in the products.
- A theoretical yield is calculated using the stoichiometry of a balanced equation & relevant mathematical relationships.
- The number of moles of limiting reactant available is used to calculate the theoretical yield of a reaction.
- If a reactant is added in excess, not all of it will react and some will be found in the final product mixture.
- A limiting reactant is one that restricts the amount of product that can form from the available particles.
Common misconception
Pupils sometimes fail to understand that excess reactant particles remain in the reaction mixture after the reaction.
Provide a balanced equation and challenge pupils to draw diagrams of a final mixture, stressing that excess particles would also be present. Challenge pupils to consider how the product could be extracted from the excess particles.
Keywords
Limiting reactant - The reactant that completely reacts, thereby determining the maximum amount of product that can be formed in a chemical reaction. All other reactants will be present in excess.
Excess reactant - Any reactant present in a greater amount than is necessary to completely react with the limiting reactant.
Theoretical yield - The maximum calculated mass of product expected to form from a given amount of reactants.
Mole - A mole of a substance contains 6.02 × 10²³ particles of it. The mass of one mole of a substance is its relative mass in grams.
Stoichiometry - The molar ratio of the reactants to the products in a chemical reaction.
Equipment
2 cm strip of Mg crucible + lid balance tongs heatproof mat, Bunsen burner, tripod clay triangle
Content guidance
- Equipment requiring safe usage.
Supervision
Adult supervision recommended.
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Video
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Starter quiz
6 Questions
the average mass of the atoms of an element compared to carbon-12
the sum of the relative atomic masses of all the atoms in a formula
the number of particles in one mole of a substance
Exit quiz
6 Questions
the reactant that completely reacts during a reaction
a reactant that is left over at the end of the reaction
the maximum calculated mass of product expected from a reaction
the unit for amount of substance