Actual Yield – IGCSE Chemistry Definition

Actual yield is the mass of product that is physically collected at the end of a chemical reaction carried out in the laboratory or in industry. It is a measured quantity, determined by weighing the product after the reaction is complete and the product has been purified.

Why actual yield matters

In theory, a reaction should produce a specific amount of product calculated from the balanced equation (the theoretical yield). In practice, the actual yield is almost always less. Comparing the two gives the percentage yield, which tells chemists how efficient a process is.

Percentage yield = (actual yield / theoretical yield) x 100

An actual yield that is close to the theoretical yield indicates an efficient process with few losses. A low actual yield suggests significant losses or incomplete reaction.

Reasons actual yield is less than theoretical yield

Several factors reduce the actual yield. Product may be lost during filtration, when some remains in the filter paper. Product may be left behind when transferring between containers. In crystallisation, not all the dissolved product may come out of solution. If the reaction is reversible, it may not reach completion. Side reactions may consume some reactants to form unwanted products instead.

Exam context

Paper 4 questions typically provide both the actual yield and the theoretical yield (or enough data to calculate the theoretical yield) and ask candidates to calculate the percentage yield. The actual yield is always given as a measured value in grams.

Worked exam question

A student reacts 10.0 g of calcium carbonate with excess hydrochloric acid. The theoretical yield of calcium chloride is 11.1 g. The student obtains 8.88 g. Calculate the percentage yield. (2 marks)

Percentage yield = (actual yield / theoretical yield) x 100 [1] = (8.88 / 11.1) x 100 = 80.0% [1].

Common mistakes

Candidates sometimes confuse actual yield with theoretical yield when substituting into the percentage yield formula. Remember: actual yield is what you actually get (the smaller number), and theoretical yield is what you should get from the calculation (the larger number). If your percentage yield exceeds 100%, you have swapped them or the product contains impurities.