October 1, 2025

What Is Percent Yield

Q: Can percent yield be over 100%?

Theoretically, no. A percent yield over 100% usually indicates an error. This often means the collected product is impure, possibly contaminated with solvent, unreacted starting materials, or byproducts, which artificially inflates its measured mass.

Q: What is the difference between actual yield and theoretical yield?

Theoretical yield is the maximum amount of product that can possibly be formed, calculated on paper from the amounts of reactants. Actual yield is the amount of product that is physically obtained when the reaction is carried out in a lab.

Q: What factors can cause a low percent yield?

Common factors include incomplete reactions where equilibrium is reached before all reactants are used, side reactions that consume reactants to make different products, and practical losses during product recovery, such as spilling or leaving material on glassware.

Q: Is a high percent yield always the goal?

While a high yield is often desirable as it indicates efficiency, the primary goal is usually high purity. Sometimes, a process with a slightly lower yield is preferred if it produces a much purer product, reducing the need for costly and difficult separation steps.

Learn what percent yield is, how to calculate it using the actual and theoretical yield formula, and why it's a crucial concept in chemical reactions.

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Defining Percent Yield

Percent yield is a measure of the efficiency of a chemical reaction. It compares the actual amount of product obtained from a reaction (the actual yield) to the maximum theoretical amount that could have been produced (the theoretical yield), and expresses this comparison as a percentage.

Section 2: The Percent Yield Formula

The formula to calculate percent yield is: Percent Yield = (Actual Yield / Theoretical Yield) x 100%. The 'actual yield' is the amount of product you physically measure after the reaction is complete. The 'theoretical yield' is the maximum amount of product you calculate using stoichiometry, based on the limiting reactant.

Section 3: A Practical Example

Suppose you are synthesizing salt (NaCl) and your stoichiometric calculations show you should theoretically produce 50 grams. After performing the experiment, you collect and weigh your product, finding you only have 45 grams. Your percent yield would be (45g / 50g) x 100%, which equals 90%.

Section 4: Importance of Percent Yield

Percent yield is a critical metric in chemistry and manufacturing. It indicates how successful and efficient a reaction was. A low percent yield might suggest issues like incomplete reactions, side reactions creating unwanted byproducts, or loss of product during purification, helping chemists refine their processes.

Frequently Asked Questions

Can percent yield be over 100%?

What is the difference between actual yield and theoretical yield?

What factors can cause a low percent yield?

Is a high percent yield always the goal?