Stoichiometry Calculator

Calculate product amounts, reactant requirements, or identify limiting reactants based on balanced chemical equations. Enter coefficients from your balanced equation and known quantities.

Core Stoichiometry Principles: 1. Mole Ratio (from balanced equation): aA + bB → cC + dD Mole ratio: a:b:c:d 2. Product Calculation: Product moles = (Reactant moles ÷ Reactant coeff) × Product coeff Product mass (g) = Product moles × Product molar mass 3. Reactant Needed: Reactant moles = (Product desired ÷ Product coeff) × Reactant coeff Reactant mass (g) = Reactant moles × Reactant molar mass 4. Limiting Reactant: For each reactant: Ratio = Moles available ÷ Coefficient Smallest ratio → Limiting reactant Determines maximum product 5. Mass-Mole Conversion: Moles = Mass (g) ÷ Molar mass (g/mol) Mass (g) = Moles × Molar mass (g/mol) 6. Percent Yield: % Yield = (Actual yield ÷ Theoretical yield) × 100%
Example 1: Combustion of Hydrogen Equation: 2H₂ + O₂ → 2H₂O Given: 4.0 g H₂ (molar mass = 2.016 g/mol) Find: H₂O produced Moles H₂ = 4.0 ÷ 2.016 = 1.984 mol Mole ratio H₂:H₂O = 2:2 = 1:1 Moles H₂O = 1.984 mol Mass H₂O = 1.984 × 18.015 = 35.7 g Example 2: Limiting Reactant Equation: N₂ + 3H₂ → 2NH₃ Given: 2.0 mol N₂, 4.0 mol H₂ Find: Limiting reactant Ratio N₂: 2.0 ÷ 1 = 2.0 Ratio H₂: 4.0 ÷ 3 = 1.33 ← Smaller (limiting!) Max NH₃ = 1.33 × 2 = 2.67 mol Excess N₂ = 2.0 - 1.33 = 0.67 mol Example 3: Reactant Needed Equation: 2Na + Cl₂ → 2NaCl Desired: 117 g NaCl (molar mass = 58.44 g/mol) Find: Na needed (molar mass = 22.99 g/mol) Moles NaCl = 117 ÷ 58.44 = 2.0 mol Mole ratio Na:NaCl = 2:2 = 1:1 Moles Na = 2.0 mol Mass Na = 2.0 × 22.99 = 46.0 g

What is stoichiometry?

Stoichiometry is the calculation of reactants and products in chemical reactions based on balanced equations. It uses mole ratios from coefficients to determine quantities needed or produced.

Why do I need to balance the equation first?

Balanced equations ensure the law of conservation of mass is satisfied. The coefficients in a balanced equation give the exact mole ratios needed for stoichiometric calculations.

What is a limiting reactant?

The limiting reactant is completely consumed first and determines the maximum amount of product that can form. Excess reactants remain after the reaction is complete.

How do I convert between grams and moles?

Use molar mass: moles = mass (g) ÷ molar mass (g/mol). For compounds, add atomic masses from the periodic table. Example: H₂O = 2(1) + 16 = 18 g/mol.

What is percent yield?

Percent yield = (actual yield ÷ theoretical yield) × 100%. Theoretical yield is the maximum possible product from stoichiometry. Actual yield is what you obtain experimentally, typically lower due to incomplete reactions or losses.

Can this calculator handle complex equations?

This calculator works for any balanced equation with known mole ratios. Enter your balanced coefficients and known quantities. For complex reactions, ensure you have accurate molar masses and coefficients.

What if I have multiple reactants?

When solving with multiple reactants, determine which is limiting by calculating moles available divided by coefficient for each reactant. The smallest ratio indicates the limiting reactant that controls product formation.

Why are mole ratios important?

Mole ratios from balanced equations are the foundation of stoichiometry. They tell you the exact proportions reactants combine and products form. Example: 2H₂ + O₂ → 2H₂O means 2 moles H₂ react with 1 mole O₂ to make 2 moles H₂O.