1.1 What is Chemistry?

12.3. Limiting Reactant and Percent Yield http://www.ck12.org

Reaction Yield

Actual vs. Theoretical Yield

The yield of a chemical reaction is the amount of certain product that is produced from given amounts of each
reactant. Theactual yieldis the amount of product that is actually produced. This value is generally not exactly equal
to thetheoretical yield, which represents the maximum amount that could be generated from the given amounts of
reactants. For example, say we performed the copper cycle as described in the introduction by starting with 1.00
grams of copper. Theoretically, the final reaction should give us back 1.00 grams of copper; this is our theoretical
yield. However, we may find that only 0.86 grams of Cu is produced; this would be our actual yield. When we
perform stoichiometric calculations, we are attempting to determine the theoretical yield based on the amounts of
reactants available. Actual yields can only be determined by performing the experiment and measuring the final
mass of product.

Percent Yield

A common way to express the yield of a reaction is as a percentage. Thepercent yieldof a reaction tells us what
percentage of the possible amount of product (the theoretical yield) was actually obtained (the actual yield). Percent
yield can be calculated using the following expression:

Percent Yield=Theoretical YieldActual Yield ×100%

Example 12.6

You calculate that 1.00 grams of copper should be produced (theoretical yield) from a given chemical process. After
you run the experiment, you find that 0.860 grams of copper is obtained. Calculate the percent yield for this process.

Answer:

Percent Yield=

0 .860 g Cu

1 .00 g Cu

×100%

=86%

The Reaction Table Method

A reaction table can be used to keep track of the masses and moles of each reaction component over the course of a
chemical reaction. For the generic reaction shown below, we can set up the followingTable12.1.

aA + bB→cC + dD

TABLE12.1:Reaction Table

A B C D

Molar Mass

Initial Mass

Initial Moles

Change in Moles -ax -bx +cx +dx

Final Moles

Final Mass