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GCSE Combined Science · key term
A reactant that is completely used up in a reaction and therefore limits the maximum amount of product that can form.
Used by AQA and Edexcel
Specification 5.3.2.4 · Paper 3
Revise: Limiting ReactantsThe limiting reactant is the reactant that is completely used up. Once it has run out, no more product can form from that reaction, even though another reactant is still available. The reactant left over is the excess reactant.
Specification Calculations involving masses · Paper 3, Paper 4
The reactant that is used up first and therefore controls the maximum mass of product formed.
Revise: Conservation of mass and quantitative reaction relationshipsThe reactant that is not in excess is the limiting reactant. Once it has all reacted, no more product can form, even if another reactant remains. Its starting mass therefore controls the maximum mass of product.
Calculate the maximum product from the limiting reactant, not from the full amount of the excess reactant.
When explaining why doubling a reactant doubles the possible product, state that it remains the limiting reactant and the other reactant is still in excess.
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