Actual Yield
Definition and meaning of Actual Yield in chemistry.
Actual yield is the real, physical amount of product you collect at the end of a chemical reaction. It is carefully measured using a scale or graduated cylinder in the laboratory. The actual yield is almost always less than the perfect theoretical yield.
In more detail
In a perfect world, a chemical reaction would turn every single starting molecule into the final product. Chemists call this perfect mathematical prediction the theoretical yield. However, real life in the chemistry lab never works out perfectly.
Several annoying physical factors will always reduce your final amount of collected product. Some of your chemical product will stubbornly stick to the sides of the glass beaker. Some of the liquid might evaporate into the room air before you can measure it.
Unexpected side reactions might also happen and create the wrong chemical entirely. The actual yield is the final physical mass you weigh on the balance after all cleaning and drying. You compare this real number to the theoretical yield to find the percent yield.
This final percentage tells you exactly how efficient your laboratory skills were. A common student mistake is trying to calculate the actual yield using math and molar masses. You can never calculate the actual yield on a piece of paper. You must actually perform the physical experiment and weigh the final product to find it.
Key facts
| Field | General Chemistry |
|---|---|
| Definition | The measured physical amount of product obtained |
| Contrasts with | Theoretical yield |
| Used to calculate | Percent yield |
| How to find it | Laboratory measurement (weighing or volume) |
| Typical value | Almost always less than theoretical yield |
Imagine you mix hydrogen gas and oxygen gas in a flask to create liquid water. Your paper math predicts a perfect theoretical yield of 18.0 grams of water. After running the experiment, you carefully collect the liquid water and place it on a digital scale. The scale reads exactly 15.3 grams of water. This measured physical value of 15.3 grams is your actual yield. You lost some water to evaporation and transferring, which explains why it is lower than the mathematical prediction.
Frequently asked questions
Why is actual yield usually less than theoretical yield?
Real reactions lose product to evaporation, messy transfers, and side reactions. It is physically impossible to collect every single atom produced.
How do you determine the actual yield in a chemistry lab?
You must run the experiment and collect the product. Then, you weigh the dried solid on a scale or measure the liquid in a cylinder.
Can you calculate the actual yield using stoichiometry?
No, you can only calculate the theoretical yield using stoichiometry math. The actual yield must be measured physically in the real world.