Theoretical Yield Calculator
Calculate the theoretical yield of a product from moles of limiting reagent.
How It Works
Enter the moles of the limiting reagent, its stoichiometric coefficient from the balanced equation, the product's stoichiometric coefficient, and the product's molar mass. The calculator first converts moles of limiting reagent to moles of product using the mole ratio, then converts moles of product to grams using the molar mass.
Formula
Worked Example: Synthesis of Water
Reaction: 2 H₂ + O₂ → 2 H₂O
- Limiting reagent: H₂, 4 mol available; coefficient = 2
- Product: H₂O; coefficient = 2; molar mass = 18.015 g/mol
- Moles of H₂O = 4 × (2/2) = 4 mol
- Theoretical yield = 4 mol × 18.015 g/mol = 72.06 g
Worked Example: Synthesis of Ammonia (Haber Process)
Reaction: N₂ + 3 H₂ → 2 NH₃. If H₂ is the limiting reagent with 6 mol:
- Moles NH₃ = 6 mol H₂ × (2/3) = 4 mol
- Molar mass NH₃ = 17.031 g/mol
- Theoretical yield = 4 × 17.031 = 68.12 g
Workflow for a Complete Yield Calculation
A complete lab yield analysis follows three steps: (1) Find the limiting reagent using the Limiting Reagent Calculator. (2) Calculate the theoretical yield here. (3) Compare to your measured actual yield with the Percent Yield Calculator. Understanding where yield is lost helps improve lab technique over time.
Common Sources of Yield Loss
Theoretical yield assumes a perfect, complete reaction. In practice, yield is reduced by: incomplete reactions (equilibrium reactions may not go to completion), side reactions that consume reactants to form unwanted products, product lost during recovery steps (filtration, extraction, transfer between containers), and experimental error in measurement. Some reactions routinely achieve 95%+ yield in experienced hands, while others naturally top out below 70%.
Frequently Asked Questions
What is theoretical yield?
Theoretical yield is the maximum amount of product that can form, calculated from stoichiometry assuming the limiting reagent reacts completely with no losses. It is the upper bound against which actual yield is compared.
Why is actual yield less than theoretical yield?
Losses occur due to incomplete reactions, side reactions, product lost during recovery steps (filtering, pipetting, crystallization), solubility losses, and measurement error. Some yield loss is expected in any real experiment.
How do I find the molar mass of a product?
Sum the atomic masses of all atoms in the product formula. For example, NH₃ = 14.007 + 3(1.008) = 17.031 g/mol. Use the Molar Mass Calculator to compute this instantly from any chemical formula.
What is percent yield and how does it relate to theoretical yield?
Percent yield = (actual yield / theoretical yield) × 100%. A percent yield of 85% means you obtained 85% of the maximum possible product. Use the Percent Yield Calculator to compute this after measuring your actual yield.
What if I don't know which reactant is limiting?
Use the Limiting Reagent Calculator first. Input moles of both reactants and their coefficients; the calculator identifies which one is limiting, which you then use as the input here.