Stoichiometry Calculator

Calculate reactant and product quantities in chemical reactions using mole ratios from balanced equations.

mol
g/mol

Quick Reference

Avogadro's Number
6.022 x 1023
particles per mole
Molar Volume (STP)
22.4 L/mol
for ideal gases at 0C, 1 atm
Water Molar Mass
18.015 g/mol
H2O
CO2 Molar Mass
44.01 g/mol
Carbon dioxide

Calculation Results

Calculated
Moles of Product
0
mol
Mass of Product
--
grams (if molar mass provided)
Number of Particles
0
molecules/atoms

Key Takeaways

  • Stoichiometry uses mole ratios from balanced equations to calculate quantities
  • The coefficients in a balanced equation represent mole ratios
  • Always balance the chemical equation before performing calculations
  • Moles = Mass / Molar Mass (use this to convert between grams and moles)
  • 1 mole = 6.022 x 1023 particles (Avogadro's number)

What Is Stoichiometry?

Stoichiometry is the calculation of reactant and product quantities in chemical reactions. The word comes from the Greek words "stoicheion" (element) and "metron" (measure). It allows chemists to predict how much product will form from given reactants, or how much reactant is needed to produce a desired amount of product.

At its core, stoichiometry is based on the law of conservation of mass - atoms are neither created nor destroyed in a chemical reaction. This means the number of atoms of each element must be the same on both sides of a balanced equation.

Example: Water Synthesis

2H2 + O2 --> 2H2O

Hydrogen (H2) 2 mol
Oxygen (O2) 1 mol
Water (H2O) 2 mol

The ratio 2:1:2 means 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water.

The Stoichiometry Formula

Moles of Product = Moles of Reactant x (Coefficient of Product / Coefficient of Reactant)
Moles = Amount of substance (mol)
Coefficient = Number in front of chemical formula in balanced equation

Additional useful formulas for stoichiometry calculations:

n = m / M

n = N / NA

n = V / Vm (for gases at STP)
n = number of moles
m = mass (g)
M = molar mass (g/mol)
N = number of particles
NA = 6.022 x 1023
V = volume (L)
Vm = 22.4 L/mol at STP

How to Solve Stoichiometry Problems (Step-by-Step)

1

Balance the Chemical Equation

Ensure equal numbers of each type of atom on both sides. Example: 2H2 + O2 --> 2H2O (4 H atoms and 2 O atoms on each side).

2

Convert Known Quantity to Moles

If given mass, divide by molar mass. If given particles, divide by Avogadro's number. If given volume of gas at STP, divide by 22.4 L/mol.

3

Use the Mole Ratio

Multiply moles of known by the ratio of coefficients (unknown/known) from the balanced equation to find moles of unknown.

4

Convert to Desired Units

Convert moles of unknown to grams (multiply by molar mass), particles (multiply by Avogadro's number), or volume (multiply by 22.4 L/mol for gases at STP).

Types of Stoichiometry Problems

Mole-to-Mole Calculations

The simplest type - directly use the mole ratio from the balanced equation. Example: How many moles of H2O form from 3 moles of H2?

Using 2H2 + O2 --> 2H2O: Moles H2O = 3 mol H2 x (2 mol H2O / 2 mol H2) = 3 mol H2O

Mass-to-Mass Calculations

Convert mass to moles, use ratio, convert back to mass. Example: How many grams of H2O form from 4 grams of H2?

  1. Convert to moles: 4 g / 2.016 g/mol = 1.98 mol H2
  2. Use ratio: 1.98 mol x (2/2) = 1.98 mol H2O
  3. Convert to mass: 1.98 mol x 18.015 g/mol = 35.7 g H2O

Limiting Reactant Problems

When given amounts of multiple reactants, the limiting reactant is the one that runs out first and determines the maximum product. Calculate the product from each reactant separately - the smaller result indicates the limiting reactant.

Applications of Stoichiometry

  • Pharmaceutical Industry: Calculating exact amounts of reactants for drug synthesis
  • Environmental Science: Determining pollution levels and remediation needs
  • Food Industry: Recipe scaling and nutritional calculations
  • Manufacturing: Quality control and production optimization
  • Forensics: Analyzing chemical evidence
  • Agriculture: Calculating fertilizer requirements

Frequently Asked Questions

A mole is a unit representing 6.022 x 1023 particles (atoms, molecules, ions, etc.). It's like a "dozen" for chemistry - just as a dozen always means 12, a mole always means 6.022 x 1023 particles. This number is called Avogadro's number.

Balancing equations ensures the law of conservation of mass is satisfied - atoms cannot be created or destroyed. The coefficients in a balanced equation represent the exact mole ratios needed for the reaction, which are essential for accurate stoichiometric calculations.

Theoretical yield is the maximum amount of product calculated from stoichiometry, assuming 100% reaction completion. Actual yield is what you actually obtain in the lab, which is typically less due to side reactions, incomplete reactions, or product loss. Percent yield = (Actual yield / Theoretical yield) x 100%.

Calculate how much product each reactant would produce if it were completely consumed. The reactant that produces the least amount of product is the limiting reactant. Alternatively, divide the moles of each reactant by its coefficient - the smallest ratio indicates the limiting reactant.

STP stands for Standard Temperature and Pressure (0 degrees C and 1 atm). At STP, one mole of any ideal gas occupies exactly 22.4 liters. This allows easy conversion between moles and volume for gaseous reactants and products in stoichiometry problems.

Yes! This calculator works for any reaction where you know the moles of one substance and the stoichiometric ratio from the balanced equation. Simply enter the moles of your known substance and the coefficient ratio (product coefficient divided by reactant coefficient) to calculate the moles of the unknown substance.