Limiting Reagent Calculator

How to use this calculator

1. Enter or choose reactant A name.
2. Enter or choose mass of A.
3. Enter or choose molar mass of A.
4. Enter or choose coefficient of A (a).
5. Enter or choose reactant B name.
6. The limiting reagent updates as you type. Use Copy result or Share to keep it.

Method

n = m ÷ M; limiting = smaller of n_A ÷ a and n_B ÷ b; product = c × min(n_A/a, n_B/b); yield = product × M_P

a, b, c

coefficients in the balanced equation aA + bB → cP

n_A, n_B

moles of each reactant

M_P

molar mass of the product

Worked example

1. n(H₂) = 10 ÷ 2.016 = 4.9603 mol → ÷ 2 = 2.4802; n(O₂) = 64 ÷ 31.998 = 2.0001 mol → ÷ 1 = 2.0001.
2. O₂ gives the smaller ratio, so it is limiting: water = 2 × 2.000125 = 4.00025 mol × 18.015 = 72.06 g.
3. H₂ used = 4.00025 mol × 2.016 = 8.0645 g, so 10 − 8.0645 = 1.94 g of H₂ is left.

In 2H₂ + O₂ → 2H₂O with 10 g H₂ and 64 g O₂, oxygen is limiting; at most 72.06 g of water forms and 1.94 g of hydrogen is left over.

What the result means

Actual yield is usually lower than theoretical; percentage yield = actual ÷ theoretical × 100.

Assumptions and limits

• The equation is balanced and the reaction goes to completion.
• Reactants are pure.
• Two reactants and one product of interest; for more reactants, compare every n ÷ coefficient ratio the same way.