Percent Yield

*Notice, kind of like the opposite of Percent Error.

Percent Yield Problems• The amount of product produced from a reaction

based on a calculation is the expected yield (or theoretical yield)

• The amount of product that is really obtained during the reaction (in a lab or industrial setting) is the actual yield (real life)

• It is useful to determine what percent of the expected yield was actually obtained.

• percent yield = actual yield x 100% expected yield

Potential reasons for differences between actual and expected yield

1. some reactants didn’t fully react2. there were side reactions that differ from the

reaction on which the expected yield was based

3. some product was lost during recovery or transfer

Example Problem

• A reaction occurs between 500.0 g of carbon disulfide and an excess amount of oxygen gas.

• The actual mass of sulfur dioxide produced is 768 g. What is the percent yield for this reaction?

• Step 1: Write the balanced equation. CS2 + 2 O2 2 SO2 + C

Notice

! You

hav

e pl

enty

of o

xyge

n, ca

n

use

up al

l CS2,

don’

t wor

ry ab

out l

imiti

ng

reag

ent!

Example Problem CS2 + 2 O2 2 SO2 + C

• Step 2: Determine the expected yield using stoichiometry

500.0 g CS2 x 1 mol CS2 x 2 mol SO2 x 64.07 g SO2 = 841.36 g SO2

76.15 g CS2 1 mol CS2 1 mol SO2

This is how much SO2 you should be able to produce (theoretical yield)

Example Problem CS2 + 2 O2 2 SO2 + C

• Step 3: Compare the actual yield to the expected yield using the percent yield equation.

• percent yield = actual yield x 100% expected yield

Percent yield = 768 g x 100% = 91.28 % (of expected) 841.36 g