Percentage Yield Example 1:
When there is a balanced chemical reaction, 138 g of H2O is produced from 16 g H2 and
we always assume that the reaction happens excess O2, what is the percent yield of H2O in
exactly the way it is written in the equation. this chemical reaction?
However, chemical reactions do not always
follow this. Chemists do not always get the Step 1. Write the balanced chemical equation
expected amount of product that they want. of the given chemical reaction.
Factors that contribute to the formation of 2H2 + O2 → 2H2O
less of more products: Step 2. Determine the actual and theoretical
yield.
Splattering or spilling of products
Occurrence of side reaction
Non-completion of the reaction as
planned
Presence of impurities
To measure the actual amount of product
produced during an experiment, chemists need
a measurement that shows how successful a
reaction is. This measurement is called percent
yield.
𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑦𝑖𝑒𝑙𝑑 = 𝑥 100% Answer: 95.83%
𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑦𝑖𝑒𝑙𝑑
Theoretical Yield Example 2:
is the expected amount of product produced in What is the percent yield of NH3 if 60g NH3 is
a chemical reaction based on stoichiometric produced from 18.0 mol h2 and excess N2?
calculation. 1. Write the balanced chemical equation of the
given chemical reaction.
Actual yield N2 + 3H2 → 2NH3
is the amount of product produced during the 2. Determine the actual and theoretical yield.
experiment. Actual yield: 60g NH3
Actual yield will always be less than the
theoretical yield because during an
experiment there is always a possibility of
error. 3. Calculate the percentage yield
Answer: 29.41%
Limiting Reactants 4. Use stoichiometry for each individual
reactant to find the mass of product produced.
When there is not enough of one reactant in a
chemical reaction, the reaction stops abruptly. 5. The reactant that produces a lesser amount
of product is the limiting reagent.
To figure out the amount of product produced,
it must be determined which reactant will limit 6. The reactant that produces a larger amount
the chemical reaction (the limiting reagent) and of product is the excess reagent.
which reactant is in excess (the excess
reagent). 7. To find the amount of remaining excess
reactant, subtract the mass of excess reagent
consumed from the total mass of excess
reagent given.
Limiting Reagent
It is the reactant that is completely used up in a
reaction and thus determines when the
reaction stops.
The limiting reagent is the one that is totally
consumed; it limits the reaction from continuing
because there is none left to react with the in-
excess reactant.
Approach #1
1. Find the limiting reagent by looking at the
number of moles of each reactant.
2. Determine the balanced chemical equation
for the chemical reaction.
3. Convert all given information into moles.
* most likely, through the use of molar mass as
a conversion factor.
4. Calculate the mole ratio from the given
information. Compare the calculated ratio to
the actual ratio.
5. Use the amount of limiting reactant to
calculate the amount of product produced.
6. If necessary, calculate how much is left in
excess of the non-limiting reagent.
Approach # 2
1. Find the limiting reagent by calculating and
comparing the amount of product each
reactant will produce.
2. Balance the chemical equation for the
chemical reaction.
3. Convert the given information into moles.
