Stoichiometry calculator (grams to grams and limiting reactant)

Enter your values. The answer and the full worked solution update as you type.

Result

Theoretical yield26.58 g
Moles of product0.476 mol
Limiting reactantreactant 2
Excess reactantreactant 1
Excess reactant left over11.99 g
M (reactant 1)159.7 g/mol
M (reactant 2)28.01 g/mol
M (product)55.84 g/mol

Do mass-to-mass stoichiometry from a balanced equation. Enter each substance as a chemical formula, such as Fe2O3, Ca(OH)2 or CuSO4·5H2O, or as a molar mass, with its coefficient. The calculator works out the molar masses, the moles, the limiting reactant, the theoretical yield of the product and the excess reactant, or the mass of the second reactant you need.

Step-by-step solution

Reaction

Fe2O3 + 3 CO → 2 Fe + …
The coefficients must come from the balanced equation.

Molar masses

M(Fe2O3) = 2·55.845 + 3·15.999 = 159.687 g/mol
M(CO) = 12.011 + 15.999 = 28.01 g/mol
M(Fe) = 55.845 g/mol

Moles and the limiting reactant

n1 = 50/159.687 = 0.3131 mol
product: 0.3131·2/1 = 0.6262 mol
n2 = 20/28.01 = 0.714 mol
product: 0.714·2/3 = 0.476 mol
Limiting reactant: reactant 2 (it gives the least product)
Excess reactant: reactant 1, 11.99 g left over

Theoretical yield

m = n·M = 0.476·55.845 = 26.58 g

Key formulas

Moles
n = m/M
Concentration
c = n/V
Mole ratio
use the coefficients of the balanced equation
Limiting reactant
the one that runs out first
Percent yield
actual / theoretical × 100%

How to solve a stoichiometry problem

  1. Balance the equation and note the coefficients.
  2. Work out each molar mass from the atomic masses: for Ca(OH)2, 40.078 + 2 × (15.999 + 1.008) = 74.09 g/mol.
  3. Convert the given masses to moles: n = m/M.
  4. Use the mole ratio from the equation to find the moles of product each reactant could make; the smallest amount comes from the limiting reactant.
  5. Convert the moles of product back to grams: m = n × M.

Questions and answers

How do I write the formulas?

Use the element symbols with the correct capitals, numbers after an element or a bracket, and round or square brackets for groups: Al2(SO4)3, K4[Fe(CN)6]. Write a hydrate with a dot or an asterisk: CuSO4·5H2O or CuSO4*5H2O.

Does the calculator balance the equation?

No. Enter the coefficients from the balanced equation yourself; the calculator then uses them for the mole ratios.

Which atomic masses are used?

The standard atomic weights (IUPAC conventional values, e.g. H 1.008, C 12.011, O 15.999, Cl 35.45). Textbooks that round them, for example Cl = 35.5, can differ in the third or fourth significant figure.

What if I only know one reactant?

Leave reactant 2 empty for a simple grams-to-grams calculation, or enter its formula without a mass to find how much of it is needed to react completely.

Practise it yourself

Stoichiometry: practice problems with step-by-step solutionsHow to solve Stoichiometry problemsStoichiometry worksheet with answers

Practise Stoichiometry

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