Percentage Yield
Lajoy Tucker
Teacher
Introduction & Definitions
Percentage Yield measures how much product is obtained in a chemical reaction compared to the theoretical maximum.
Definition: Percentage Yield = (Actual Yield/Theoretical Yield)
Actual Yield: The amount of product actually obtained from the reaction.
Theoretical Yield: The maximum possible mass of product, based on stoichiometric calculations.
Basic Principles
A 100% yield means the reaction produced all the product it theoretically could.
Common reasons for a percentage yield below 100% include:
Incomplete reactions
Side reactions forming unwanted products
Loss during purification (e.g. filtration, evaporation)
Product remains in the reaction vessel
How to calculate percentage yield for a reaction:
Step 1: Write a balanced equation.
Step 2: Calculate the theoretical yield using molar ratios from the equation.
Step 3: Use the actual yield (often given in grams).
Step 4: Use the formula: Percentage Yield = (Actual Yield/Theoretical Yield)
Worked Examples
Example 1:
In the reaction:
A student reacts of with excess . The mass of hydrogen gas collected was . What is the percentage yield?
Answer
Step 1: Moles of used;
Step 2: Theoretical moles of (1:1 ratio with );
Step 3: Theoretical mass of ;
Step 4: Use percentage yield formula;
Example 2:
of calcium carbonate were added to an excess of sulfuric acid.
Calculate the mass of produced in this reaction assuming a 95% yield.
Answer
Moles of used
mass /
Theoretical moles of (1:1 stoichiometry)
Theoretical mass of
Actual mass at 95% yield
m(actual) (to 3 s.f.)
of
Practice Question
of reacts, and of is formed. What is the percentage yield?
Answer
Ratio
Theoretical moles of
Mass
% Yield %
Key Tips & Reminders
Always base theoretical yield on the limiting reagent.
Convert masses to moles – do not directly divide the masses provided
No answer provided.