
home	test	drill	game	contact

Yield

Key Concepts

Yield is the mass of product formed in a chemical reaction.
Actual yield is the mass of product formed in an experiment or industrial process.
Theoretical yield is the mass of product predicted by the balanced chemical equation for the reaction.
Percentage yield = (actual yield ÷ theoretical yield) x 100
Optimum yield is the best possible yield achieved for a set of given reaction conditions.
For a chemical reaction which goes to completion:
actual yield = theoretical yield
so, percentage yield = 100%
For a chemical reaction at equilibrium:
actual yield < theoretical yield
so, percentage yield < 100%
For a chemical reaction at equilibrium, actual yield can be affected by factors such as:
temperature
concentration
pressure and volume (gaseous systems)

Percentage Yield Calculations

Example 1: Calculating Percentage Yield

112g of nitrogen gas reacts with hydrogen gas to produce 40.8g of ammonia gas according to the equation given below:

N_2(g) + 3H_2(g)

2NH_3(g)

Calculate the percentage yield of ammonia.

Actual yield of ammonia (NH₃) = 40.8g
Theoretical yield of ammonia (NH₃) is calculated using the equation:
moles = mass ÷ molar mass
From the balanced chemical equation the mole ratio N₂:NH₃ is 1:2
moles NH₃ = 2 x moles N₂
moles NH₃ = 2 x (mass N₂ ÷ molar mass N₂) = 2 x 112 ÷ 28 = 8 moles
theoretical yield NH₃ = predicted mass NH₃
predicted mass NH₃ = moles NH₃ x molar mass NH₃ = 8 x 17 = 136g
Percentage yield = (actual yield ÷ theoretical yield) x 100
percentage yield NH₃ = (40.8 ÷ 136) x 100 = 30%

Example 2: Calculating Mass of Product from Yield

Ammonia can be produced from hydrogen gas and nitrogen gas according to the equation below:

N_2(g) + 3H_2(g)

2NH_3(g)

Calculate the mass of ammonia produced if 168 g of nitrogen gas produces a yield of 45%.

Percentage yield = 45%
Calculate the theoretical yield of NH₃:
From the balanced chemical equation the mole ratio N₂:NH₃ is 1:2
moles NH₃ = 2 x moles N₂
moles NH₃ = 2 x (mass N₂ ÷ molar mass N₂) = 2 x 168 ÷ 28 = 12 moles
theoretical yield NH₃ = predicted mass NH₃
predicted mass NH₃ = moles NH₃ x molar mass NH₃ = 12 x 17 = 204 g
Calculate the actual yield:
percentage yield = (actual yield ÷ theoretical yield) x 100
Re-arranging this equation gives:
actual yield = theoretical yield x percentage yield ÷ 100
actual yield of NH₃ = 204 x 45 ÷ 100 = 91.8 g

Factors Affecting Actual Yield

Le Chatelier's Principle can be used to predict the affect of changes in temperature, concentration, gas pressure and volume on actual yield.

Factor Conditions Actual Yield % Yield

reactant concentration increase increases increases

reactant concentration decrease decreases decreases

temperature increase exothermic reaction decreases decreases

endothermic reaction increases increases

temperature decrease exothermic reaction increases increases

endothermic reaction decreases decreases

gas pressure increase mol reactant_(gas) > mol product_(gas) increases increases

mol reactant_(gas) < mol product_(gas) decreases decreases

gas pressure decrease mol reactant_(gas) > mol product_(gas) decreases decreases

mol reactant_(gas) < mol product_(gas) increases increases

Practice Questions

For AUS-e-TUTE members:

Click on the Yield Calculations drill link:
Yield Calculations drill
Enter your username and password if prompted.
Click the "New Question" button to begin the drill.
Worked solutions are provided if you need some help!

Not an AUS-e-TUTE Member?

Join AUS-e-TUTE.
About AUS-e-TUTE membership
(information for students and teachers)

Search this Site

You can search this site using a key term or a concept to find, tutorials, tests, exams, learning activities (games), drills, worksheet and quiz wizards.