Stoichiometry & gases · SL/HL
Limiting reagent
Use stoichiometric ratios to identify the limiting reagent.
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Number formats & units
Use decimal dots in datasets. Single values also accept decimal commas and scientific notation such as 1.2e-3 or 1.2 × 10⁻³.
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Result & working
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Interpretation & assumptions
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Formula & example
The relationship
What the variables mean
| Symbol | Meaning |
|---|---|
| Stoichiometric coefficient from the balanced equation. | |
| Available reaction extent set by the smallest n/ν. |
Worked example
- Amount of reactant A / mol
- 0.50
- Coefficient of A
- 2
- Amount of reactant B / mol
- 0.30
- Coefficient of B
- 1
- Coefficient of desired product
- 2
- Product molar mass / g mol⁻¹ (optional)
- 18.015
0.5 mol product
Follow the example steps
- A: n/ν = 0.5/2 = 0.25
- B: n/ν = 0.3/1 = 0.3
- ξ = min(0.25, 0.3) = 0.25 mol
- n(product) = ξν = 0.25 × 2 = 0.5 mol
- m(product) = nM = 0.5 × 18.015 = 9.0075 g
Common mistakes
Compare amount divided by the stoichiometric coefficient.
Incorrect approach
2A + B → P; n_A = n_B = 1 mol: n_A = n_B
Correct approach
n_A/2 = 0.5 mol < n_B/1 = 1 mol
More checks before you submit
- Do not compare raw mole amounts if coefficients differ.
- Theoretical yield assumes the limiting reactant is fully consumed according to the stated reaction.
Method notes
Convert all reactant quantities to moles first. The smallest amount divided by its coefficient identifies the limiting reactant.