Stoichiometry Calculator
Determine the theoretical and actual yield of a chemical reaction from reactant mass, molecular weights, stoichiometric ratio, and percent yield. Ideal for lab planning and synthesis work.
About this calculator
Stoichiometry converts between masses of reactants and products using molar ratios from a balanced equation. The formula used here is: actual yield = ((reactant_mass / reactant_mw) × stoic_ratio × product_mw) × (percent_yield / 100). First, reactant mass is converted to moles (reactant_mass / reactant_mw). Those moles are scaled by the stoichiometric ratio to find moles of product formed. Multiplying by the product's molecular weight converts back to grams, giving the theoretical yield. Finally, multiplying by percent yield / 100 accounts for real-world losses. This framework applies to any single-step reaction and is foundational in synthetic chemistry, pharmaceutical manufacturing, and industrial processing.
How to use
Suppose 10 g of hydrogen (H₂, MW = 2 g/mol) reacts with excess nitrogen to form ammonia (NH₃, MW = 17 g/mol). The balanced equation N₂ + 3H₂ → 2NH₃ gives a stoichiometric ratio of 2/3 ≈ 0.667. Assume 85% yield. Step 1: moles of H₂ = 10 / 2 = 5 mol. Step 2: moles of NH₃ = 5 × 0.667 = 3.33 mol. Step 3: theoretical mass = 3.33 × 17 = 56.67 g. Step 4: actual yield = 56.67 × (85/100) = 48.17 g. Enter these values into the calculator to confirm.
Frequently asked questions
How do I find the stoichiometric ratio from a balanced chemical equation?
The stoichiometric ratio is the coefficient of the product divided by the coefficient of the reactant in the balanced equation. For N₂ + 3H₂ → 2NH₃, the ratio of NH₃ to H₂ is 2/3. Always balance the equation first before reading off coefficients. If you are working with a limiting reagent, calculate the ratio for each reactant separately and use the one that gives the smallest theoretical yield.
What is the difference between theoretical yield and actual yield in a chemical reaction?
Theoretical yield is the maximum mass of product that could form if the reaction went to 100% completion with no losses. Actual yield is what you physically collect after the reaction, which is always less due to side reactions, incomplete conversion, and handling losses. Percent yield = (actual yield / theoretical yield) × 100 quantifies this efficiency. A percent yield above 100% indicates a measurement or calculation error, often from residual solvent or impurities in the product.
Why is the limiting reagent important in stoichiometry calculations?
The limiting reagent is the reactant that runs out first, capping how much product can form regardless of how much of the other reagents are present. Identifying it requires converting all reactant masses to moles and comparing them against the stoichiometric ratios. The reactant producing the fewest moles of product is the limiting reagent. Ignoring it leads to overestimated yields and wasted materials in industrial or laboratory synthesis.