Stoichiometry Calculator

Stoichiometry uses balanced equation coefficients as mole ratios to convert between reactants and products. The mole bridge: grams → moles → mole ratio → moles → grams.

⚖️ Stoichiometry📐 Mole Ratio🧪 Reactions

Moles (or grams) of A

Molar mass of A (g/mol, if using grams)

Coefficient of A

Coefficient of B

Molar mass of B (g/mol)

Please enter valid values.

Formula & Reference

Variable	Symbol	Formula	Units
Mole Ratio	—	mol A / mol B = coeff A / coeff B	mol
Moles of A	n₂	n₁ × (coeff B / coeff A)	mol
Mass of B	m₂	n₂ × M₂	g
Key Step	—	Always convert to moles first!	mol

Step-by-Step Examples

Example 1

Combustion of Methane

CH₄ + 2O₂ → CO₂ + 2H₂O. How many mol CO₂ from 3 mol CH₄?

Ratio CO₂/CH₄ = 1/1
mol CO₂ = 3 × 1 = 3 mol
Mass CO₂ = 3 × 44.01 = 132 g

✓ 3 mol CO₂, mass = 132 g

Example 2

Ammonia Synthesis

N₂ + 3H₂ → 2NH₃. Mol NH₃ from 5 mol H₂?

Ratio NH₃/H₂ = 2/3
mol NH₃ = 5 × (2/3) = 3.333 mol
Mass = 3.333 × 17.03 = 56.77 g

✓ 3.33 mol NH₃, mass = 56.8 g

Example 3

From Grams

2H₂ + O₂ → 2H₂O. How many g H₂O from 8.00 g H₂?

mol H₂ = 8.00/2.016 = 3.968 mol
mol H₂O = 3.968 × (2/2) = 3.968 mol
mass H₂O = 3.968 × 18.02 = 71.49 g

✓ 71.5 g of water produced

Real-World Applications

🏭

Chemical Manufacturing

Plants calculate exact raw material quantities using stoichiometric ratios.

🚀

Rocket Fuel

Fuel-oxidizer ratios in rockets are optimized using stoichiometry.

🧪

Synthesis Planning

Lab chemists calculate theoretical yield before running reactions.

♻️

Environmental Chemistry

Pollution abatement calculations use stoichiometry for scrubber design.

Common Mistakes to Avoid

⚠️

Not converting to moles first

The mole ratio applies to MOLES, not grams. Always convert grams to moles, apply ratio, then convert back if needed.

⚠️

Using wrong coefficients

Read the balanced equation carefully. Coefficients are the mole ratios. If unbalanced, balance first.

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Confusing A and B in ratio

mol B = mol A × (coeff B / coeff A). The substance you want goes on top of the fraction.

Frequently Asked Questions

What is a mole ratio? ▾

The ratio of coefficients of two substances in a balanced equation. For 2H₂ + O₂ → 2H₂O: mol H₂O / mol H₂ = 2/2 = 1. So 1 mol H₂ gives 1 mol H₂O.

How do I handle multi-step stoichiometry? ▾

Calculate moles of the intermediate product from step 1, then use it as the starting material for step 2. Convert to moles at each step.

What is the mole bridge? ▾

The sequence: g A ÷ M₂ = mol A × (coeff B/coeff A) = mol B × Mᴮ = g B. Every stoichiometry problem follows this path.

Do coefficients change with different amounts? ▾

No. Coefficients are fixed by the balanced equation. Only the amounts of reactants and products change proportionally.

What if the equation is not balanced? ▾

Balance it first using conservation of atoms and charge. Stoichiometry calculations are invalid with unbalanced equations.

Related Chemistry Calculators

Formula Explorer connections

Interpretation: This relationship converts chemical amount, mass, composition or balanced-equation ratios into a reaction quantity. Assumption: Use a balanced reaction, consistent units and the correct molar mass. Purity, side reactions and limiting reagents can change experimental results.

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