How to Calculate Stoichiometry

Stoichiometry uses balanced chemical equations to calculate the amounts of reactants consumed and products formed in a chemical reaction. It's the quantitative backbone of chemistryβ€”essential for labs, industrial chemistry, and pharmaceuticals.

The Mole Road Map

Mass β†’ (Γ· molar mass) β†’ Moles β†’ (Γ— mole ratio) β†’ Moles β†’ (Γ— molar mass) β†’ Mass

Step-by-Step Example

Reaction: 2Hβ‚‚ + Oβ‚‚ β†’ 2Hβ‚‚O How many grams of water form when 4 grams of hydrogen reacts completely?

Step 1: Convert grams of Hβ‚‚ to moles. Molar mass of Hβ‚‚ = 2 g/mol 4 g Γ· 2 g/mol = 2 moles Hβ‚‚

Step 2: Use mole ratio from balanced equation. 2 mol Hβ‚‚ : 2 mol Hβ‚‚O β†’ ratio = 1:1 Moles of Hβ‚‚O = 2 Γ— (2/2) = 2 moles Hβ‚‚O

Step 3: Convert moles of water to grams. Molar mass of Hβ‚‚O = 18 g/mol 2 moles Γ— 18 g/mol = 36 grams of water

Finding the Limiting Reagent

The limiting reagent is the reactant that runs out first, determining how much product forms.

Example: You have 3 mol Hβ‚‚ and 2 mol Oβ‚‚. Which is limiting?

  • Hβ‚‚ can make: 3 Γ— (2/2) = 3 mol Hβ‚‚O
  • Oβ‚‚ can make: 2 Γ— (2/1) = 4 mol Hβ‚‚O

Hβ‚‚ produces less product β†’ Hβ‚‚ is the limiting reagent. Maximum product = 3 mol Hβ‚‚O = 54 grams.

Theoretical vs. Actual Yield

% Yield = (Actual yield / Theoretical yield) Γ— 100%

If you actually collected 50 g of water: % yield = 50/54 Γ— 100 = 92.6%

Use our stoichiometry calculator for any balanced chemical equation.