Stoichiometry Calculator

What is Stoichiometry?

Stoichiometry is the calculation of the quantities of substances that participate in a chemical reaction.

It is based on the Law of Conservation of Mass: Atoms are not created or destroyed, but only rearranged.

Key Concepts:
  • Mole: A unit for amount of substance (6.022 × 10²³ particles)
  • Molar Mass: The mass of 1 mole of a substance (g/mol)
  • Molar Ratios: The ratio between reactants in an equation
  • Limiting Reagent: The substance that runs out first
Tip: Use this calculator to quickly convert between mass, moles, and ratios.
Formulas
Mass from Moles:
m = n × M
m = mass (g), n = moles (mol), M = molar mass (g/mol)
Moles from Mass:
n = m / M
n = moles (mol), m = mass (g), M = molar mass (g/mol)
Molar Ratios:
n_A / n_B = a / b
n_A, n_B = moles, a, b = coefficients from equation
Avogadro's Constant:
N_A = 6.022 × 10²³ mol⁻¹
The number of particles per mole


Examples
Example 1: Oxygen (O₂)
• Molar mass: M = 32.00 g/mol
• Moles: n = 2.5 mol
• Mass: m = 2.5 × 32.00 = 80.0 g
Example 2: Water (H₂O)
• Molar mass: M = 18.016 g/mol
• Mass: m = 36.032 g
• Moles: n = 36.032 / 18.016 = 2.0 mol
Example 3: Hydrogen Combustion
2H₂ + O₂ → 2H₂O
• 4 g H₂ (2 mol) reacts with 32 g O₂ (1 mol)
• Ratio nH₂ : nO₂ = 2 : 1
Example 4: Methane Combustion
CH₄ + 2O₂ → CO₂ + 2H₂O
• 16 g CH₄ (1 mol) requires 64 g O₂ (2 mol)
• Ratio nCH₄ : nO₂ = 1 : 2
Technical Background
Stoichiometry Fundamentals

Stoichiometry is based on three fundamental concepts:

1. The Mole (Unit of Amount of Substance)

A mole is a collection of exactly 6.022 × 10²³ particles. This incredibly large number (Avogadro's constant) links the atomic world to measurable quantities in the laboratory.

2. Molar Mass

Molar mass is the mass of one mole of a substance. It has the unit g/mol. The molar mass in g/mol is numerically equal to the atomic mass in u (atomic mass units).

3. Molar Ratios

In a chemical reaction, the substances are in specific molar ratios to each other, defined by the coefficients of the balanced chemical equation.

Limiting Reagent

In practical reactions, one of the substances is used up first. This substance determines how much product can be formed. All other substances are in excess.

Practical Applications:
  • Calculation of reaction quantities in laboratories and industry
  • Optimization of chemical processes
  • Cost calculation for raw materials
  • Environmental protection and waste management
Common Mistakes:
  • Using incorrect molar mass (element vs. compound)
  • Chemical equation not balanced
  • Units not considered (g vs. kg, mol vs. mmol)
  • Decimal separator confusion (period vs. comma)

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