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GCSE Chemistry · key term
A reactant present in a greater amount than is needed to react completely with the limiting reactant, so some remains when the reaction stops.
Used by AQA, Edexcel and OCR
Specification 4.3.2.4 · Paper 1
A reactant present in a greater amount than is needed to react completely with the limiting reactant, so some remains unreacted.
Revise: Limiting ReactantsAdding more of an already excess reactant cannot make any additional product because there is no limiting reactant left for it to react with. Adding more of the limiting reactant can increase the amount of product, but only until the other reactant becomes limiting.
Specification 1.52 · Paper 1, Paper 2
Revise: Limiting ReactantsAny other reactant supplied beyond the amount required is an excess reactant, and some of it remains after the limiting reactant has gone.
A reactant present in more than the amount needed to react completely with the other reactant.
Specification C3.1k · Paper 1 (Foundation), Paper 3 (Higher)
A reactant present in a greater amount than is required to react with the limiting reactant, so some remains when the reaction stops.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A reactant present in more than the amount required by the balanced equation, so some remains when the reaction stops.
When asked why product formation stops, state that the limiting reactant has been completely used up, so the remaining excess reactant cannot form any more product.
Calculate the product from the limiting reactant. A calculation based on an excess reactant would predict more product than can actually form.
Once the limiting reactant has been identified, base the amount of product on it. An excess reactant cannot produce more product after the limiting reactant is exhausted.
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