GCSE Chemistry (AQA)

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Limiting Reactants Calculations

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Quantitative chemistry Use of amount of substance in relation to masses of pure substances

Limiting Reactants Calculations

6:44 Limiting Reactant
Spec 4.3.2.4
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  • The limiting reactant determines the amount of product formed in a chemical reaction.
  • The reaction stops when the limiting reactant is used up, and other reactants are in excess.
  • Example: In bread making, flour can be the limiting reactant.
  • Reacting mass calculations help determine the mass of product formed by identifying the limiting reactant.
  • Example calculation: Reaction between magnesium and sulfuric acid to find maximum hydrogen mass.
  • Steps to calculate maximum mass of iron from iron oxide and aluminum:
  • 1. Calculate moles of both reactants using moles = mass / relative formula mass.
  • 2. Identify the limiting reactant using the balanced equation ratio.
  • 3. Use the ratio between limiting reactant and product to find moles of product.
  • 4. Calculate the mass of the product using mass = moles x relative formula mass.
  • Example: Iron oxide and aluminum reaction, aluminum is the limiting reactant.
  • Final calculation: Maximum mass of iron formed is 2.35 grams.
  • Understanding the effect of a limiting reactant is crucial for exams, in terms of moles or masses in grams.

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