Limiting Reagent & Yield

Type a reaction and how much of each reactant you have. The equation is balanced for you, the limiting reagent — the one that runs out first — is found, and you get the theoretical yield of every product and what is left of the rest. Weighed what you made? Add it for the percent yield and the atom economy.

StoichiometryLimiting reagentYieldLab

Inputs

Input examples

Type _ for a subscript (H_2 gives H₂) and ^ for a charge (Fe^3+ gives Fe³⁺); -> becomes an arrow. Plain H2O works too. The keyboard button in the field has a chemistry tab with elements, charges, states and arrows. Write the reaction with -> between reactants and products and + between substances, for example N2 + H2 -> NH3. Capital letters matter (Co is cobalt, CO is carbon monoxide). Coefficients are optional: an unbalanced equation is balanced automatically. Then enter the amount of each reactant in grams or moles; leave one empty if you have plenty of it. To get the percent yield, choose the product you collected and enter its mass (dry).

Reaction

N_{2}+H_{2}\rightarrow NH_{3}

Product you collected

Mass you collected — optional

Limiting Reagent, Yield and Atom Economy

A balanced equation is a recipe in moles. N₂ + 3 H₂ → 2 NH₃ says that every mole of nitrogen needs three moles of hydrogen. You rarely have exactly that ratio, so one reactant runs out first: the limiting reagent. It decides how much product can form; the others are left over, in excess.

To find it, convert every amount to moles and divide by its coefficient. That number, the extent of reaction ξ, tells how many times the reaction “recipe” could run on that reactant alone. The smallest one wins. The amount of product you would get if everything reacted perfectly is the theoretical yield.

In practice you collect less: some reactant does not react, side reactions make something else, and product is lost while filtering and drying. The percent yield compares what you collected with the theoretical yield. The atom economy looks at the equation itself: even at 100% yield, by-products carry atoms away. Reactions with a high atom economy waste less, a key idea of green chemistry.

n = m / Mgrams to moles

smallest n/νlimiting

one product onlyatom economy 100%

yield > 100%product still wet or impure

How Far Each Reactant Lasts

limiting: runs out first

in excess

bar height: moles ÷ coefficient (ξ)

Result

Enter a reaction and the amounts above

Collected vs Possible

yield

theoretical yield

what you collected

Before and After

Substance	M (g/mol)	Start	Change	End

Worked Techniques

Grams to Moles, then n / ν

Divide each mass by its molar mass, then each amount in moles by its coefficient. The smallest result is the limiting reagent, even when it is not the smallest mass.

Example: 28 g of N₂ limits 10 g of H₂ (4.96 mol).

Theoretical Yield

Multiply the extent of reaction by the product’s coefficient for its moles, then by its molar mass for grams.

Example: 2.0 g salicylic acid can give 2.609 g of aspirin.

Percent Yield and Atom Economy

Divide what you collected by the theoretical yield. The atom economy only depends on the balanced equation: the Haber process makes nothing but ammonia, 100%.

Example: thermite gives iron with only 52% atom economy: the rest leaves as Al₂O₃.

Sources & Verification

References

S. S. Zumdahl & S. A. Zumdahl, Chemistry, 10th ed., Cengage Learning, 2018 — Ch. 3 (Stoichiometry: balancing, limiting reactant, theoretical and percent yield).
P. Atkins, L. Jones & L. Laverman, Chemical Principles: The Quest for Insight, 7th ed., W. H. Freeman, 2016 — Fundamentals H, L and M (equations, reaction stoichiometry, limiting reactants).
B. M. Trost, “The atom economy — a search for synthetic efficiency”, Science 254 (1991) 1471–1477 — the definition of atom economy.
CIAAW / IUPAC, Standard atomic weights — conventional values, as on the Molar Mass page.