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Year 10 - Science

Limiting reactants (RAM 1 d.p.)

Calculations involving masses

Unit Summary

This unit covers writing chemical formulae, balancing equations, and using the conservation of mass. It includes calculating moles, empirical formulae, relative formula masses, and theoretical yields. Emphasis is on stoichiometry, concentration, gas volumes, and using standard form.

Lesson Summary

You will learn to identify a reactant as an excess or limiting reactant and use that information to calculate a theoretical yield.

Key Notes

  • 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 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.

Vocabulary To Learn

  • 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 is 6.02 × 10²³ particles of it. The mass of a mole of a substance is its relative mass in grams.
  • stoichiometry: The molar ratio of the reactants to the products in a chemical reaction.

Common Mistakes To Avoid

  • Pupils sometimes fail to understand that excess reactant particles remain in the reaction mixture after the reaction.

3 Quick Questions (With Answers)

1. Explain the scientific idea in this lesson using two key 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.

2. Define this scientific word and use it in context. '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. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Pupils sometimes fail to understand that excess reactant particles remain in the reaction mixture after the reaction. Correction: 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.

More Lessons In This Unit

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