Limiting reactant calculator (limiting reagent), stoichiometry
Limiting reactant, masses of products formed and leftovers, from an equation balanced along the way.
Result
O2
- Balanced equation
- 2 H2 + O2 → 2 H2O
- Maximum extent
- ξ = 2.0001 mol
Products formed (theoretical)
Reactant balance
- M(H2)
- 2.016 g/mol
- M(O2)
- 31.998 g/mol
- M(H2O)
- 18.015 g/mol
Notes (3)
O2 is the limiting reactant. Maximum extent: 2.0001 mol.
Theoretical amounts, for a complete reaction with no loss.
Some molar masses rest on a conventional atomic weight: for fourteen elements (including H, C, N, O, S and Cl), IUPAC publishes an interval, since isotopic composition varies with the sample’s origin.
Calculation, assumptions and sources
OverviewFrom the equation, balanced along the way, and the available amounts in grams or moles: limiting reactant (smallest “moles ÷ coefficient” ratio), maximum extent, mass of each product formed and leftover of each excess reactant.
From the equation, balanced along the way, and the available amounts in grams or moles: limiting reactant (smallest “moles ÷ coefficient” ratio), maximum extent, mass of each product formed and leftover of each excess reactant. A reactant with no amount is assumed to be in excess, and the assumption is shown.
Method & formulasn = m / M (mass → amount of substance)
The limiting reactant has the smallest “available moles ÷ stoichiometric coefficient” ratio. That ratio is the maximum extent ξ, in moles. Each product forms as ν × ξ, each reactant is consumed as ν × ξ, and the leftover is the difference. Balancing gives the minimal integer coefficients, by linear algebra over exact fractions, as in the balancer tool.
- Limiting reactant
- the one that runs out first and stops the reaction; its final leftover is zero.
- Extent (ξ)
- the number of “times” the reaction, as written with its coefficients, has occurred, in moles.
- Theoretical amount
- what a complete reaction would give, with no side reaction and no loss. The yield is the mass obtained divided by this theoretical mass.
Validity domainThe reaction is assumed complete: a reaction limited by a chemical equilibrium (esterification, dissociation) does not reach these amounts.
The reaction is assumed complete: a reaction limited by a chemical equilibrium (esterification, dissociation) does not reach these amounts. Neutral species, four reactants at most; redox half-equations and ionic equations, which require charge conservation, are not handled. Molar masses use IUPAC abridged standard atomic weights (terrestrial isotopic averages), fourteen of which are conventional values, flagged when they apply.
Finding the limiting reactantWith 10 g of H₂ and 64 g of O₂ in 2 H₂ + O₂ → 2 H₂O, oxygen is limiting despite its larger mass: 4.96 mol of H₂ (M = 2.016 g/mol) against a coefficient of 2 gives a ratio of 2.48, while 2.00 mol of O₂ against a coefficient of 1 gives 2.00.
With 10 g of H₂ and 64 g of O₂ in 2 H₂ + O₂ → 2 H₂O, oxygen is limiting despite its larger mass: 4.96 mol of H₂ (M = 2.016 g/mol) against a coefficient of 2 gives a ratio of 2.48, while 2.00 mol of O₂ against a coefficient of 1 gives 2.00.