Percentage yield calculator with working

• Percentage yield: the theoretical yield is 5.6 g and you collect 4.2 g. $4.2 \div 5.6 \times 100 = 75\%$.
• Actual yield: a reaction has an 80% yield and a theoretical yield of 12 g. Actual $= 80 \div 100 \times 12 = 9.6$ g.
• Theoretical yield: 3 g of product is a 60% yield. Theoretical $= 3 \div 0.6 = 5$ g.

1. Write the balanced equation.
2. Find the moles of the limiting reactant: $n = \text{mass} \div M_r$.
3. Use the ratio in the equation to find the moles of product.
4. Multiply by the product's $M_r$ to get the mass.

Example: heating 10 g of calcium carbonate ($M_r = 100$): CaCO₃ → CaO + CO₂. Moles $= 10 \div 100 = 0.1$, so 0.1 mol of CaO ($M_r = 56$), a theoretical yield of 5.6 g. Our moles calculator helps with steps 2 and 4.

• The reaction may be reversible and not go to completion.
• Some product is lost when it's separated from the mixture (filtering, transferring between containers).
• Some reactants may take part in unexpected side reactions.

A yield over 100% usually means the product is still wet or contains impurities, so dry it to a constant mass and weigh again.

Percentage yield is about how much product you actually collect. Atom economy is about how much of the reactants' mass ends up in the desired product in theory, from the equation alone. A reaction can have a high yield but a low atom economy (lots of waste products), or the other way round. Find atom economy with our atom economy calculator.

• Dividing theoretical by actual (giving more than 100%).
• Using the mass of a reactant instead of the theoretical mass of product.
• Forgetting to use the mole ratio from the equation.

Practise with our percentage yield questions and reacting masses questions.

• Find the limiting reactant first: the theoretical yield comes from whichever reactant runs out.
• Give the percentage to the number of significant figures the data supports (usually 2 or 3).
• If a question asks why the actual yield was low, give a specific reason such as product lost during filtration, not just "human error".