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Reaction stoichiometry calculator

Reaction stoichiometry from a balanced chemical equation.

Enter a balanced equation, identify the known and target species, and convert a measured amount into target moles, mass and formula units.

03

Balanced equation → stoichiometric quantity

Moles and reaction calculator

Enter a balanced reaction, choose a known substance, and calculate the target quantity.

target moles = known moles × (target coefficient ÷ known coefficient)

Calculated quantity for H2O3 mol
54.045 gtarget mass1.8066e+24particles / formula units3 molknown amount after conversion

Mathematical formula

Apply the balanced-equation mole ratio

nB = nA × (νB ÷ νA)mB = nBMB

Worked problems

Follow the units through each step.

1

Formation of water

Problem: For 2H₂ + O₂ → 2H₂O, how much water forms from 3.00 mol H₂ when oxygen is in excess?

  1. Read coefficients: ν(H₂) = 2 and ν(H₂O) = 2.
  2. Use n(H₂O) = 3.00 × (2 ÷ 2) = 3.00 mol.
  3. M(H₂O) = (2 × 1.008) + 15.999 = 18.015 g·mol⁻¹.
  4. Calculate mass: 3.00 × 18.015 g.

Answer: 3.00 mol H₂O, corresponding to 54.045 g H₂O.

2

Ammonia synthesis

Problem: For N₂ + 3H₂ → 2NH₃, what mass of NH₃ corresponds to 28.014 g N₂ when H₂ is in excess?

  1. Convert N₂ mass to moles: 28.014 g ÷ 28.014 g·mol⁻¹ = 1.000 mol.
  2. Apply the ratio: n(NH₃) = 1.000 × (2 ÷ 1) = 2.000 mol.
  3. M(NH₃) = 14.007 + (3 × 1.008) = 17.031 g·mol⁻¹.
  4. Calculate target mass: 2.000 × 17.031 g.

Answer: 2.000 mol NH₃, corresponding to 34.062 g NH₃.