Limited Reactants and percent yield

Bell Ringer

How many
NH3
molecules
can you
form?

3H2 + N2 → 2NH3

Before and After Reaction 1

All the hydrogen and nitrogen atoms combine.

Before the reaction

After the reaction

Open Ended

What was your answer for the bell ringer?

Essential Question

Which
compound
is limiting?

3H2 + N2 → 2NH3

Open Ended

Which element was limiting?

Before and After Reaction 2

Before the reaction

After the reaction

Standard SC.912.P.8.9

•Apply the mole concept and the
law of conservation of mass to
calculate quantities of
chemicals participating in
reactions.

Objectives

•Define limiting Reactant, excess
reactant

•Follow a particle diagram to
determine excess and limited

DEFINITIONS

•LIMITING REACTANT

• Completely consumed in a chemical reaction

• Determines the amount of product formed

• The reactant that produces the least amount of

product

DEFINITIONS

• THEORETICAL YIELD

The amount of product that can be made based on the
amount of the limiting reactant

• ACTUAL YIELD

The amount of product actually or experimentally
produced

• THE PERCENT YIELD

%yield = (actual/theoretical) x 100

Limiting Reactants

•

Limiting Reactant

• used up in a reaction

• determines the amount of product

•

Excess Reactant

• added to ensure that the other reactant is completely used up

• cheaper & easier to recycle

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

•

Percent yield: The ratio of actual yield (from an

experiment) to theoretical yield (from stoichiometric

calculations) expressed as a percent.

+

8 car bodies

48 tires

8 cars

plus 16 tires

excess

Limiting Reactants

CB + 4 T CBT4

Example with a grilled cheese:
2 slices of bread + 3 slices of cheese →
1 grilled cheese

I have 100 slices of
cheese, how many slices
of bread will I need if I
want to use all the
cheese?

• I have 15 slices of

bread, how many
grilled cheese
sandwiches can I
make?

What is the

limiting reactant?

What is the excess

reactant?

N2 + H2 → NH3

• Balance the equation

• Set up the ratio between

Nitrogen and ammonia

• Solve

• Repeat between

hydrogen and ammonia

• How many moles of NH3

will be produced from 2
moles of nitrogen and 2
moles of hydrogen?

• Which is limited

reactant?

Learning Check #1 Percent Yield

• During the lab you calculated

that you could produce 3.5 grams
copper, but you only produced 3
grams. What is your percent
yield?

Multiple Choice

What is your answer from the learning check #1?

• 85.7%

• 117%

• 100%

• 50%

Learning Check #2 Percent Yield

• The theoretical yield of NaCl was

2.5 g and the actual yield was 1.9
g. What was the % yield?

Volume L

Volume L
22.4 L
22.4 L

Concept Map

Multiple Choice

What was your answer for Learning Check #2

• 100%

• 75%

• 76%

• 132%

Learning Check #3 (Limited
Reactants)

In the reaction of 3CuCl2 + 2Al →
2AlCl3 + 3Cu, you have 5 grams
aluminum and 5 grams copper
chloride, how many moles of copper
can you produce?

Multiple Choice

What is my answer to Learning Check #3?

• 0.277 moles copper chloride

• 0.037 moles copper chloride

• 0.185 moles copper chloride

• 0 moles

Learning Check #4(Limited
Reactants)

C2H4 + 3 O2 → 2 CO2 + 2 H2O

If you start with 0.155 moles C2H4 and
0.155 moles O2, how many liters of CO2
can you produce?

Multiple Choice

What is your answer for learning check #4?

• 6.94 moles carbon dioxide

• 5 moles carbon dioxide

• 0 moles carbon dioxide

• 0.103 moles carbon dioxide

Open Ended

How many CO₂ molecules did you form? What is the limited reactant?

Learning Check #5

• A mixture of CO(g) and O2(g) is placed in a container as shown in

the pictures. A reaction occurs to form CO2. How many CO2
molecules may be formed? What is your limited reactant?

2 CO + O2 → 2 CO2