Percentage Yield
Simple Explanation
Percentage yield compares the actual amount of product you get from a reaction to the theoretical (maximum possible) amount predicted by the balanced equation, as a percentage.
Why Do We Need It?
Real reactions almost never produce 100% of the theoretical maximum — percentage yield tells chemists and industry how efficient a reaction actually is.
Formula
Percentage Yield
% yield = (actual yield / theoretical yield) × 100
How much of the maximum possible product a reaction actually produced, as a percentage.
- actual yield
- — the amount of product actually obtained
- theoretical yield
- — the maximum possible amount of product, predicted from the balanced equation
When to use it: Whenever you need to measure how efficient a reaction was at converting reactants into the desired product.
Worked Example
Calculate percentage yield
A reaction has a theoretical yield of 20 g of product. The actual yield obtained is 15 g. What is the percentage yield?
Why Does This Work?
Dividing what you actually obtained by the maximum theoretically possible, then converting to a percentage, directly measures how close a real reaction came to its perfect, loss-free outcome.
Real-Life Example
Why medicines are expensive to manufacture
Pharmaceutical reactions often have percentage yields well below 100%, with product lost at each step of a multi-step synthesis.
Low percentage yield across several manufacturing steps compounds, meaning a large amount of expensive starting material is needed to produce a much smaller final amount of medicine.
Practice
A reaction's theoretical yield is 50 g and the actual yield is 40 g. What is the percentage yield?
EasyCommon mistake
Dividing theoretical yield by actual yield instead of the other way around — this would give a percentage yield greater than 100%, which isn't possible for a real reaction.
Quick Review
- % yield = (actual yield / theoretical yield) × 100
- Percentage yield is always 100% or less in practice.
- Lower yield means more starting material is needed for the same amount of product.