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Senior High
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Physical Science
Quarter 1 - Module 3
Week 5: Collision Theory and the Factors
Affecting the Reaction Rate
Week 6: Limiting Reactant and Percent
Yield
i
Department of Education ● Republic of the Philippines
ii
Physical Science – Grade 12
Alternative Delivery Mode
Quarter 1 - Module 3: Week 5: Collision Theory and the Factors Affecting the
Reaction Rate
Week 6: Limiting Reactant and Percent Yield
First Edition, 2020
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iii
Senior High School
Physical Science
Quarter 1-Module 3
Week 5: Collision Theory and the Factors
Affecting the Reaction Rate
Week 6: Limiting Reactant and Percent Yield
This instructional material was collaboratively developed and
reviewed by educators from public schools. We encourage teachers
and other education stakeholders to email their feedback,
comments, and recommendations to the Department of Education
at cagayandeoro.city@deped.gov.ph
We value your feedback and recommendations.
Department of Education ● Republic of the Philippines
iv
TABLE OF CONTENTS
Page
What This Module is About
v
What I Need to Know
v
How to Learn from this Module
v
Icons of this Module
vi
What I Know
1
Lesson 1 – Collision Theory and Factors Affecting the Rate of Reaction
3
What’s In
What’s New:Effect of Surface Area/Particle Size of the Reactants
What is It
What’s New:Effect of Concentration on Reaction Rates
What is it
What’s New:Effect of Temperature on Reaction Rates
What is it
What’s New: Effect of Catalyst on Reaction Rates
What is it
What’s More: Identifying Scenarios
What’s More: Real-life Applications
What I Have Learned: True or False)
Lesson 2 – Limiting Reactants and Percent Yield
What I Need to Know
What’s In
What’s More: Solving Limiting Reactant Problems
What’s More: Solving Percent Yield Problems
What’s More: Why Percent Yield is Usually Less than 100%?
What I Have Learned
What I Can Do: Essay
Assessment
Key to Answers
References
3
4
5
6
7
7
8
9
9
10
11
11
12
12
13
15
17
18
18
19
20
22
23
What This Module is About
This module discusses how the collision theory is used to explain the effects
v
of concentration, temperature, particle size, and presence of catalyst on the reaction
rate. The limiting reactant and the amount of product that is formed in the chemical
reaction are also discussed. Understanding the concepts in this module will enable
us to explain the chemical changes that are happening around us in our daily lives.
The following are the lessons contained in this module
Lesson 1- The Collision Theory and the Factors Affecting Reaction Rate
Lesson 3- Limiting Reactant and Percent Yield
What I Need to Know
After going through this module, you are expected to:
1. Use simple collision theory to explain the effects of concentration,
temperature, and particle size on the rate of reaction
(S11/12PS-IIIf-23)
2. Define catalyst and describe how it affects reaction rate
(S11/12PS-IIIf-24)
3. Calculate the percent yield of a reaction (S11/12PS-IIIh-26)
4. Determine the limiting reactant in a reaction and calculate the amount of
product formed (S11/12PS-IIIh-27)
How to Learn from this Module
To achieve the learning competencies cited above, you are to do the
following:
•
•
•
Take your time reading the lessons carefully.
Follow the directions and/or instructions in the activities and exercises
diligently.
Answer all the given tests and exercises.
vi
Icons of this Module
vii
What I Know
ii
i
MULTIPLE CHOICE
Directions: Read and understand each item and choose the letter of the correct answer.
Write your answers on a separate sheet of paper.
1. What do you call the minimum amount of energy needed to start a chemical
reaction?
A. Activation energy.
C. Reaction mechanism energy
B. Energy of the reaction.
D. The entropy of reaction
2. Which statement best describes the Collision theory?
A. All collisions lead to chemical reactions.
B. Most collisions lead to chemical reactions.
C. Very few reactions involve particle collisions.
D. Effective collisions lead to chemical reactions.
3. Which is/are necessary for successful collisions to occur?
I. Favorable collision geometry.
II. Sufficient kinetic energy.
III. Large change in enthalpy (∆H).
A. I only
C. II and III only
B. I and II only
D. I, II and III
4. Which of the following will decrease the number of effective collisions during a
chemical reaction?
A. Adding a catalyst.
C. Decreasing the temperature.
B. Increasing the surface area.
D. Increasing reactant concentrations.
5. Which of the following will increase the reaction rate?
A. Adding a catalyst
B. Decreasing temperature
C. Using lumps instead of powder
D. Decreasing the concentration of an acid
6. Crushing a solid into a powder will increase the reaction rate. Why?
A. The particles will collide with more energy.
B. The powdered form has more surface area.
C. The activation energy barrier will be lowered.
D. The orientation of colliding particles will be improved.
7. Why does increasing the temperature of the reactants increase the reaction rate?
A. Heat energy increases the size of the molecules of reactants, and therefore
the molecules react more frequently.
B. Heat energy helps to lower the amount of overall energy that is required for
the reaction to occur.
C. Heat energy causes some of the reactants to evaporate, thereby increasing
the concentration of the reactants.
D. Heat energy causes the particles of the reactants to move faster, therefore,
react with each other more frequently.
8. Enzymes are an important component in the human body. Most chemical
reactions do not occur or will proceed slowly without enzymes. What are
enzymes?
A. Biological Catalyst
B. Simple elements
C. Chemicals that increase the surface area
D. Molecules used to increase concentration.
9. How does a catalyst makes a chemical reaction faster?
A. It makes lower energy pathways available.
B. It increases the concentration of products.
C. It increases the concentration of the reactants.
D. It binds to enzymes to release substrate.
10. What happens to a catalyst in a chemical reaction?
A. It evaporates.
B. It remains unchanged.
C. It is incorporated into the reactants.
D. It is incorporated into the products.
11. Which of the following substances act as catalysts in the body?
A. carbohydrates
B. lipids
C. nucleic acids
D. enzymes
12. What is a limiting reactant?
A. The reactant that makes the product.
B. The reactant that is fully consumed prevents more products from being made.
C. The reactant that is used up last and prevents more products from being
made.
D. The substance that is in excess that doesn't get used up as a reactant.
13. For the reaction: C5H12 + 8 O2 → 5 CO2 + 6 H2O
If 2 moles of C5H12 & 8 moles of O2 react, what is the limiting reactant?
A. C5H12
B. O2
C.
CO2
D.
H2O
14. Consider the reaction in # 13, how many moles of CO 2 is produced in the
reaction?
A. 5
B. 6
C.7
D.8
15. What is the mass of hydrogen gas (H 2) formed when 25 grams of aluminum
reacts with excess hydrochloric acid according to this balanced chemical
equation:
2 Al +6 HCl →2 Al Cl3 +3 H 2
A. 0.41 g
B. 1.2 g
C. 1.8 g
2
35
(Hint : 11 H ; 27
13 Al ; 17 Cl ; )
D. 2.8 g
Lesso
n
1
Collision Theory and the Factors Affecting
Reaction Rate
Chemical reactions are all around us. We witness it every day- combustion,
digestion, photosynthesis, cooking, and many more. Have you ever wondered what
causes a chemical reaction? What are needed for a chemical reaction to occur?
For this lesson, we will discuss the Collision Theory that provides a qualitative
explanation of chemical reactions and the rates at which they occur. It explains why
some chemical reactions are faster while others
are slow.
What’s In
This theory states that in order for a
chemical reaction to occur, the reactant particles
(atoms or molecules) must effectively collide. Effective collision means that
reactants collide with each other with sufficient energy (known as the activation
energy) and proper orientation. The absence of any one of these factors will not
result in a chemical reaction.
The Collision Theory further tells us that the rate of a chemical reaction is
proportional to the number of successful collisions between the molecules of the
reactants. The more often reactant molecules collide effectively, the more often they
react with one another and the faster the reaction rate.
Activation Energy- the minimum amount of energy used to initiate a chemical
reaction. If the reactant particles do not possess the required activation energy when
they collide, they simply bounce off each other without reacting.
Figure 1. Combustion of LPG Gas- a chemical
reaction with a fast reaction rate.
3
Figure 2. Rusting of Iron- a chemical reaction
with a slow reaction rate.
Factors that Affect Reaction Rates
Chemical reactions proceed at different rates. Some reactions can happen at
very fast rates like the combustion of LPG gas in kitchens, while others may occur at
a slower rate over several years like the rusting of iron.
There are four (4) factors that affect the speed of a chemical reaction. These
are the (1) surface area/particle size of the reactants, (2) concentration of the
reactants, (3) temperature, and (4) the presence of catalysts. The collision theory
is used to explain the effects of these factors on the reaction rate.
We shall investigate the effects of these factors through activities. These
activities mostly use household materials so that students will be able to perform
them at home.
1. Effect of Surface Area/Particle Size of the Reactants on Reaction Rates
Let us determine the effect of the surface area/ particle size of the reactants to
the reaction rate by doing Activity 3.1.1
What’s New
Activity 3.1.1.The Effect of Surface Area/ Particle Size on Reaction Rates
Objective: Investigate the effect of concentration on the rate of a reaction.
Materials:
2 Similar cups
2 effervescent tablets ((E.q. Alka seltzer tablets, Berocca, Panadol, Redoxan)
Mortar and pestle
Stopwatch
Procedure:
Part A. Whole Tablet
1. Fill one cup with 100 mL of room temperature water.
2. Drop one (1) whole effervescent tablet into the cup of water. Record the time the
effervescent tablet completely dissolves. Record data in Table 3.1.1.
Part B: Powdered Tablet
1. Place one (1) effervescent tablet into a mortar and grind to a fine powder.
2. Transfer the powdered tablet into a container.
3. Fill one cup with 100 mL of room temperature water.
4. Put the powdered tablet in the cup of water. Record the time the effervescent
tablet completely dissolves. Record data in Table 3.1.1.
4
Table 3.1.1: The Effect of Surface Area/ Particle Size on Reaction Rates
Reaction Condition
Time the tablet was fully
dissolved
Observations
Whole effervescent tablet
in a cup of water
powdered effervescent
tablet in a cup of water
Guide Questions:
1. Which reaction is faster? Why?
Answer:_______________________________________________________
_____________________________________________________________
2. How does the surface area/ particle size affect the reaction rate?
Answer:_______________________________________________________
______________________________________________________________
What is It
In Activity 3.1.1,
we used various particle sizes to compare the rates of reaction.
You observed that the powdered effervescent tablet dissolves faster in a cup of
water than the whole tablet. Why? Although they have the same mass, they differ in
surface area. Breaking the reactant into smaller pieces increases its surface area
allowing more particles to be available for a collision.
In collision theory, as more particles collide the frequency of collision also
increases and more likely results to a faster reaction rate. The reaction becomes
faster as particles get smaller.
5
2. Effect of Concentration on Reaction Rates
The concentration tells us how much solute there is in a solution. Activity 3.1.2
will help us determine its effect on the reaction rate.
What’s New
Activity 3.1.2: Effect of Concentration on Reaction Rates
Objective: to investigate the effect of concentration on the rate of a
reaction.
Materials:
2 similar cups
6 mL pure Vinegar
1.5 mL of Water
2 spoonful of Baking soda
Procedure:
1. In one cup, use pure vinegar (3mL) and place one spoonful of baking
soda. Record in Table 3.1.2 the time it takes for the reaction to
happen.
2. In another cup, add pure vinegar (1.5mL) and water (1.5 mL) before you
add the spoon full of baking soda. Record reaction time in Table 3.1.2.
Table 3.1.2: Effect of Concentration on Reaction Rates
Concentration
Total Time of Reaction
Observations
Pure Vinegar
50% vinegar + 50% water
Guide Questions
1. Which reaction had the fastest rate? Why?
Answer:_______________________________________________________
______________________________________________________________
2. Explain what could be occurring at the molecular level in each example. (How
are the molecules moving or acting?)
Answer:_______________________________________________________
______________________________________________________________
3. Why substances with high concentrations react faster than substances with
low concentrations?
Answer:_______________________________________________________
______________________________________________________________
6
What is It
In Activity 3.1.2, the pure vinegar has more concentration than the
vinegar solution which makes the reaction rate faster. The rates of many
reactions depend on the concentrations of the reactants. Reaction rates
usually increase when the concentration of one or more of the reactants
increases. Increasing the concentration means more reactant particles are
in a given space (volume) which increases the likelihood of collisions
between them. The increased frequency of collisions results in a faster
reaction rate.
For a chemical reaction to occur, a certain number of energized
molecules must be equal to or greater than the activation energy. As the
concentration increases, the number of molecules with the minimum
energy required also increases, and thus the reaction rate increases.
3. Effect of Temperature on Reaction Rates
Temperature is the measure of the degree of hotness or coldness of an
object. It is a measure of the average kinetic energy of the particles in an object.
What is its effect on the reaction rates? Let us find out in Activity 3.1.3.
What’s New
Activity 3.1.3: The Effect of Temperature on Reaction Rates
Objective:
1. To investigate the effect of temperature on reaction rates
Materials:
Hot water
Cold water
2 clear similar glasses
Stopwatch/Timer
Effervescent tablet (E.q. Alka seltzer tablets, Berocca, Panadol, Redoxan)
Procedure:
Part A: Hot Water
1. Fill a clear glass with exactly 100 mL of hot water.
2. Take the temperature of the hot water by using a laboratory thermometer and
record your data in Table 3.1.3.
3. Drop 1 effervescent tablet into the hot water. Measure the time it takes for the
tablet to fully dissolve. Record your data in Table 3.1.3.
Part B. Cold Water
1. Fill a clear glass with exactly 100 mL of cold water.
Use the thermometer to take the temperature of the cold water and record it in Table
3.1.3.
2. Drop 1 effervescent tablet into the cold water. Measure the time it takes for the
tablet to fully dissolve. Record your data in Table 3.1.3.
7
Table 3.1.3: The Effect of Temperature on Reaction Rates
Temperature Time the tablet was
of water
fully dissolved
Observations
Hot water
Cold water
Guide Questions:
1. In which glass of water does the effervescent tablet dissolved faster? Why?
Answer:_______________________________________________________
______________________________________________________________
2. What happens to the reactant molecules as you increase the temperature of
the reaction?
Answer:_______________________________________________________
_____________________________________________________________
3. How does the temperature affect the reaction rate?
Answer:_______________________________________________________
______________________________________________________________
What is It
The effervescent tablet dissolved faster in hot water than in
cold water. Therefore, the reaction rate is directly proportional to the temperature.
The reaction becomes faster as the temperature gets higher.
Increasing the temperature of the reactants increases the kinetic energy that it
possesses causing the particles to move faster. As they move faster, the frequency
of collision between them increases. This gives the reactants enough energy to
overcome the activation energy thus making the reaction faster.
8
4. Effect of a Catalyst on Reaction Rates
9
What’s New
Activity 3.1.4: Effect of a Catalyst on Reaction Rates
Objective:
1. to investigate the effect of a catalyst on reaction rate
Materials:
Hot water
Hydrogen peroxide (H2O2)
2 Test tubes
Manganese dioxide
Procedure:
1. Place 10mL of hydrogen peroxide (H2O2) in 2 separate test tubes. Place one
test tube in a hot water bath. Note the rate bubbles form.
2. Add a pinch of manganese dioxide in the second test tube. Note the rate
bubbles form.
Guide Questions:
1. How will you compare the rate at which bubbles were produced?
Answer:_______________________________________________________
______________________________________________________________
2. What happened to the test tube added with manganese dioxide? What do you
call the manganese dioxide?
Answer:_______________________________________________________
______________________________________________________________
3. What is a catalyst? How does it affect the reaction rate?
Answer:_______________________________________________________
______________________________________________________________
What is It
In Activity 3.1.4, manganese dioxide catalyzes the reaction. A
catalyst is a substance that speeds up the rate of a chemical reaction without
itself being consumed by the reaction. Once the reaction is over, you'd have exactly
the same amount of catalyst as you did at the start.
The addition of a catalyst provides a new reaction pathway that
offers a lower activation energy. Lowering the activation energy enables more
reactant molecules to collide with enough energy to overcome the smaller energy
barrier.
Enzymes are proteins that act as catalysts for biochemical reactions.
Table 3.1.5 Examples of Enzymes
10
Enzyme
Produced
by
CARBOHYDRATE
DIGESTION
Salivary amylase
Site of
Action
Optimum
pH
Digestion
Salivary glands
Mouth
Neutral
Starch+ H2O→maltose
Pancreatic amylase
Pancreas
Small Intestine
Basic
Starch+ H2O→maltose
Maltase
Small Intestine
Small Intestine
Basic
Maltose+ H2O→glucose+ glucose
Small Intestine
Small Intestine
Basic
Lactose+ H2O→glucose+
galactose
Gastric Glands
Stomach
Acidic
Protein+ H2O→peptides
Trypsin
Pancreas
Small Intestine
Basic
Protein+ H2O→peptides
peptidases
Small Intestine
Small Intestine
Basic
peptide+ H2O→amino acids
Pancreas
Small Intestine
Basic
Small Intestine
Small Intestine
Basic
RNA and DNA +H2O→
nucleotides
Nucleotide + H2O→ base+
sugar+phosphate
Pancreas
Small Intestine
Basic
Lactase
PROTEIN DIGESTION
Pepsin
NUCLEIC ACID
DIGESTION
Nuclease
Nucleosidases
FAT DIGESTION
Lipase
Fat droplet + H2O→
monoglycerides+ fatty acids
What’s More
Activity 3.2.1
Identifying the Scenarios
Identify whether the following scenarios will increase or decrease the reaction
rate. Write your answer on the space provided before each number.
_____________1. Breaking a reactant into smaller pieces.
_____________2. Increasing the temperature.
_____________3. Putting foods on the fridge.
_____________4. Diluting solutions.
_____________5. Adding heat.
11
What’s More
Acti vity 3.2.2
Real Life Applications
Which factor affecting reaction rate is depicted in each of the following
situation/scenario. Write your answers in the second column of the table below.
Situation/Scenario
1. Protein is broken down in the stomach by the
enzyme pepsin.
2. More bubbles appear when a concentrated
solution of hydrochloric acid is added to a
magnesium strip than when a dilute solution of
the acid is added.
3. Raw potatoes are cut into thin slices for
cooking.
4. Blowing air on a campfire to help get it
going.
5. Grains of sugar dissolves quickly in water.
6. Smaller pieces of charcoal are used to grill
food.
7. Meat is stored in a refrigerator to last longer.
8. Acid rain erodes marble faster.
9. Protease is used to tenderize meat.
10. Leaving a glass of milk on the table causes it
to spoil easily.
Factor Affecting Reaction Rate
What I Have Learned
TRUE or FALSE: Write T if the statement is true and write F when it is false. Write
your answer before each number.
____________1. Collision theory states that particles have to collide with sufficient
energy to react.
____________2. Starter energy is the minimum amount of energy required for a
successful collision.
____________3. Adding heat will increase the reaction rate.
____________4. Grains of sugar has a greater surface area than a cube of
sugar of the same mass.
____________5. Usually lowering the temperature will slow down a reaction.
12
Lesson
2
Limiting Reactant and Percent Yield
What I Need to Know
In the previous lesson, you were able to understand how a chemical reaction
occurs and what happens in a chemical change. You were able to realize that for a
chemical reaction to happen, the reactant particles must collide with enough energy
and proper orientation. You also learned that chemical reactions speed up or slow
down by the four factors affecting reaction rate.
Aside from knowing those concepts, you must also know what limits a
chemical reaction, when a chemical reaction stops and how much product forms
after a chemical reaction. In this lesson, you will know how to determine the limiting
reactant and how to compute for the percent yield.
At the end of this lesson, you are expected to:
1. Explain the concept of limiting reactant, excess reactant, theoretical yield,
actual yield and percent yield.
2. Identify the limiting reactant in the chemical reaction.
3. Identify the excess reactant in the chemical reaction,
4. Solve for the amount of product formed after the reaction.
5. Compute for the percent yield.
13
Wh
at’s In
In your lower grades, you dealt with ideal Stoichiometry calculations where
reactants combine with one another in a specific molar ratio described by the
balanced equation. In that case, you assumed that all the reactants are consumed in
the reaction and are completely converted into products. However, in most chemical
reactions, reactants are present in mole ratios that are not the same as the ratio of
the coefficients in the balanced chemical equation. The quantities of reactants are
rarely exact. Usually there is too much of one reactant, and not enough of another.
Therefore, not all reactants are completely converted into products. One reactant is
completely consumed in the reaction while the other one is in excess.
Limiting Reactant
The limiting reactant is the reactant that is completely used-up or consumed
in a chemical reaction. It is called the limiting reactant because it limits the amount of
product formed in the reaction. Once it is consumed, the reaction stops.
Excess Reactant
The excess reactant is the reactant other than the limiting reactant. It is the
reactant that is left-over after chemical reaction.
How to Find the Limiting Reactant?
How can you determine which reactant is limited? Consider the reaction
between molten sulfur (S8) and chlorine gas (Cl2) to form disulfur dichloride
according to this equation:
S8 (l)+¿ 4 Cl2 (g)→ 4 S2Cl2 (l)
If 200.0 g of sulfur reacts with 100 g chlorine, what is the limiting reactant?
What mass of disulfur dichloride is produced?
This kind of problem is an example of a limiting reactant problem since you
are given the quantities of both the reactants and you are asked to calculate for the
amount of the product. To solve limiting reactant problems, consider the following
steps:
Step 1: Write down the known and the unknown quantities in the problem.
Given: mass sulfur = 200.0 g
mass chlorine= 100 g
Unknown: a.) limiting reactant
b.) mass of disulfur dichloride (S2Cl2)
Step 2: Balance the chemical equation.
In the problem, the chemical equation is already balanced.
14
Step 3: Convert mass of reactants to moles.
Use the molar mass ( inverse ) as a conversion factor
Step 4: Calculate the mole ratio of the reactants.
To determine the actual ratio of moles, divide the available moles of chlorine by
the available moles of sulfur which you calculated in Step 3.
Actual
Ratio
To get the stoichiometric ratio, divide the moles of chlorine to the moles of
sulfur from the balanced chemical equation.
S8 (l)+¿ 4 Cl2 (g)→ 4 S2Cl2 (l)
Stoichiometric ratio=
4 moles Cl 2
1 mole S8
Step 5: Compare the actual ratio to the stoichiometric ratio
The actual ratio tells us that we need 1.808 mole of Cl2 for every mole of S8. In
the stoichiometric ratio, 4 moles of Cl2 is needed for every mole of S8. Since
only1.808 moles of chlorine is actually available for every 1 mole of sulfur instead of
the 4 mole of chlorine required by the balanced chemical equation then chlorine is
the limiting reactant.
How to Get the Amount of Product Formed?
Use the calculated amount of moles of the limiting reactant to determine the
moles of product formed. Then, convert the number of moles of product to its mass.
Going back to the problem, we are asked of the mass of disulfur dichloride
produced in the reaction. To calculate:
mole vale of
the limiting
reactant
x
mole ratio of the
limiting reactant
and the product
molar mass of
the product
x
=
Mass of the
Product
190.4 g of S2Cl2
Now you know that 190.4 g of S2Cl2 is produced when 1.410 mol Cl2 reacts
with an excess of S8. ( Note: This is the theoretical yield)
15
13
How to get the Excess Reactant?
What about the reactant sulfur, which you know is in excess? How much of it
actually reacted? You can calculate the mass of sulfur needed to react completely
with 1.410 mol of chlorine using a mole-to- mass calculation. The first step is to
multiply the moles of chlorine by the mole ratio of sulfur to chlorine to obtain the
number of moles of sulfur. Remember, the unknown is the numerator and the known
in the denominator.
Now, to obtain the mass of sulfur needed, 0.3525 mol S8 is multiplied by the
conversion factor that relates mass and moles, molar mass.
Knowing that 90.42 g S8 is needed, you can calculate the amount of sulfur left
unreacted when the reaction ends. Since 200.0 g of sulfur is available and only
90.42 g of sulphur is required, the excess mass is:
200.0 g S8(g) available −¿ 90.42 g S8(g) needed ¿ 109.6 g S8(g) in excess.
What’s More
Solving Limiting Reactant Problems
Instruction: Show your complete solutions legibly in one (1) whole sheet of paper.
(Total Score: 25 points)
1. Given the following reaction:
Mg (OH)2 +2 HCl →Mg Cl2 +2 H2 O
If 16.0 g of Mg (OH )2 and 11.0 g of HCl are combined.
a. What is the limiting reactant? ( 5 points)
b. How many grams of Mg Cl 2+ ¿ will be produced? ( 5 points)
2. The reaction between solid white phosphorus and oxygen produces solid
tetraphosphorusdecoxide (P4O10).
a. Write the balanced chemical equation of the reaction. ( 5 points)
b. Determine the mass of tetraphosphorusdecoxide (P 4O10) formed if 25.0
phosphorus (P4) and 50.0 g of oxygen (O2) are combined. ( 5 points)
g of
c. How much of the excess reactant remains after the reaction stops? (5 points)
16
How to get the Percent Yield?
Chemical reactions don’t always give us the exact amount of product we are
expecting. Usually, we yield amount of product that is less than our expected
outcome. To determine how much product we obtained, we get the percent yield.
In many calculations you have been practicing, you have been asked to
calculate the amount of product that can be produced from a given amount of
reactant. The answer you obtained is called the theoretical yield of the reaction. The
theoretical yield is the maximum quantity of a product derived from a given quantity
of reactant. The actual yield is the amount of a product produced when an
experiment is performed. Hence, the percent yield of product is the ratio of the
actual yield ( amount of a product from the experiment) to the theoretical yield
expressed as a percent. It effectively states how much of the reactants become
product in a chemical reaction.
Sample Problem1:
The decomposition of magnesium carbonate forms 15 grams of magnesium
oxide (MgO) in an experiment based on this equation:
MgCO3 → MgO + CO2
The theoretical yield is 19 grams. What is the percent yield of magnesium oxide?
Solution:
Given: actual yield=15 g MgO
theoretical yield = 19 g MgO
Unknown: % Yield
Solution:
% yield=
15 g MgO
x 100
19 g MgO
%yield =79 %
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Sample Problem 2:
What is the percent yield of sodium sulfate when 32.18 g of sulfuric acid
reacts with excess sodium hydroxide to produce 37.91 g of sodium sulfate?
Solution:
Given: mass H 2 S O 4 =32.18 g
mass Na 2 S O4 ( actual yield )=37.91 g
In the problem, it is clearly stated that sodium hydroxide is the excess
reactant. Therefore, sulphuric acid is the limiting reactant. Use the limiting reactant to
get the theoretical yield of sodium sulphate.
The theoretical yield is 46. 59 g Na2 S O4
% yield=
37.91 g Na 2 S O 4
x 100=81.37 %
46.59 g Na 2 S O 4
Therefore, the percent yield is 81.37%
What’s More
Solving Percent Yield Problem
Instruction: Show your complete solutions legibly in a one (1) whole sheet of paper.
(Total Score:10 points)
1. When potassium dichromate (K2CrO4) is added to a solution containing
0.500 g silver nitrate (AgNO3), solid silver chromate (Ag2CrO4) is formed.
( Note: Be sure to write down the balanced chemical equation.)
a) Determine the theoretical yield of the silver chromate precipitate.
(5 points)
b) If 0.455 g of silver chromate is obtained, calculate the percentage yield.
( 5 points)
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What’s More
Why Percent Yield is Usually Less than 100%?
List down four (4) possible reasons why percent yield is usually less than 100%.
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What I Have Learned

The theoretical yield is the maximum quantity of product derived from a
given quantity of reactant. It is calculated from the balanced chemical
equation.
 The actual yield is the amount of product actually produced when an
experiment is performed.

Percent yield is the ratio of actual yield to theoretical yield expressed
as percent.
 The limiting reactant is the reactant that is completely consumed during a
chemical reaction. Reactant that remain after the reaction stops are called
excess reactants.
Percent yield is determine by this formula:
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What I Can Do
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Essay: Write a minimum of 100 words essay on the topic presented
below.
Question: How can an understanding of the limiting reactant, excess reactant
and percent yield help manufacturing companies?
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Assessment
MULTIPLE CHOICE
Directions: Read and understand each item and choose the letter of the correct
answer. Write your answers on a separate sheet of paper.
1.
What is the effect of temperature rise on reaction rate?
A. It increases molecular concentration and slows reaction rate.
B. It increases the number of effective collisions among reactants, thus
increasing the reaction rate.
C. It decreases the system's energy and limits how much further reaction can
take place.
D. It decreases the number of collisions and the energy of molecules to limit
further reaction.
2. Your Science teacher demonstrates an interesting chemical reaction in your
class. The teacher dissolves zinc strips in a container with concentrated
hydrochloric acid. The teacher then added more hydrochloric acid in the
container and added more pieces of zinc strips. What factor will NOT affect the
reaction rate?
A. The amount of hydrochloric acid.
C. The concentration of reactants.
B. The surface area of the Zinc.
D. The size of the container.
3. When the concentration of reactant molecules increases, the rate of reaction
increases. What is the best explanation for this? As the reactant concentration
increases,
A. the rate constant increases.
B. the activation energy increases.
C. the average kinetic energy of molecules increases.
D. the frequency of molecular collisions increases.
4. What does a catalyst do?
A. Stabilises a reaction
B. Cools the reaction down
C. Increases the rate of reaction
D. Increases the concentration of the reaction
5. It helps to speed up a reaction but does not take part in the chemical reaction.
A. Catalyst
B. Coefficient
C. Combustion
D. Reactants
6. Which among these conditions will increase the rate of a chemical reaction?
A. Increased temperature and decreased concentration of reactants.
B. Increased temperature and increased concentration of reactants.
C. Decreased temperature and decreased concentration of reactants.
D. Decreased temperature and increased concentration of reactants.
7. Grinding a seltzer tablet into powder increases the rate of reaction due to
increased
A. Concentration
B. Reactants
C. Surface area
D. Temperature
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8. Why are many types of foods stored in refrigerators?
A. At lower temperature, the chemical reactions that spoil food occur slower
than usual.
B. Refrigerators also contain enzymes that slow the rate of reactions that spoil
the food.
C. The volume inside the refrigerator decreases the concentration of the food
particles, allowing them to decompose more slowly.
D. Bacteria do not grow well in dark places.
9. Which reactant controls the amount of product formed in a chemical reaction?
A. Composition
B. Excess
C. Limiting
D. Mole
10. The ______________ yield is the maximum amount of product possible in a
reaction. This determines the amount of product that should be produced in a
perfect setting.
A. Actual
B. Percent
C. Stoichiometry
D. Theoretical
11. In a laboratory experiment, the sodium (Na) metal was reacted with chlorine gas
(Cl2), and the observed actual yield was 13.0 grams. What is the percent yield if
the calculated theoretical is 12.5 grams?
A. 100%
B. 104%
C. 96%
D.1.04%
12. Which of the following statements is most useful in determining the limiting
reactant in a chemical reaction.
A. Calculate the bond energies.
B. Determine the molar mass of the products.
C. Determine the masses of 100 mol of each reactant.
D. Calculate the mass of a single product formed from each reactant.
13. What amount of the excess reagent remains when 6.00 g of CS gas react with
10.0 g of Cl2 gas in this reaction?
3 Cl2 ( g )+C S 2(g) → S 2 Cl 2(l) +C Cl 4
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(Hint:126C , 35
17Cl , 16 S )
A. 2.42 g
B. 2.77 g
C. 3.58 g
D. 4.00 g
14. If 25.0 grams of Zn are reacted with 17.5 g of HCl according to this equation:
1
35
Zn+ 2 HCl → Zn Cl2 + H 2
(Hint:65
30 Zn , 1 H , 17 Cl )
How many grams of H2 will be produced?
A. 0.382 g
B. 0.479 g
C. 0.765 g
D. 25.0 g
15. In the reaction below, 8.0 g of H 2 react with 9.0 g of O2. Which of the following
statements is true?
2 H2 + O2
2 H 2O
A. The equation is not balanced.
B. The H2 is the limiting reactant.
C. The O2 is the limiting reactant.
D. 2.0 moles of H2O would be produced.
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(Hint:168O , 11 H )
Answer Key
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References
Books
Chang, Raymond. Essential Chemistry. Reprint, Boston: McGraw-Hill, 2000.
Dapul,Gian Karlo R.,Salazar, Maria Kristina. Teaching Guide for Senior High School
Physical Science Quezon City, Philippines: Commission on Higher Education.
2016.
Valdoz, Meliza, Marites Aquino, Jonna Biong, and Mylene Andaya. Science Links
Worktext For Scientific And Technological Literacy. Manila: Rex Bookstore,
Inc. 2017.
Website
Lawson, Peggy, and Stephen Lower. "The Collision Theory". Chemistry Libretexts,
2020.
https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_T
extbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/
Kinetics/Modeling_Reaction_
Kinetics/Collision_Theory/The_Collision_Theory.
Mikulecky, Peter J, Katherine Brutlag, Michelle Rose Gilman, and Brian Peterson.
"How To Calculate Percent Yield In A Chemical Reaction - Dummies". Dummies,
2020. https://www.dummies.com/education/science/chemistry/how-to-calculatepercent-yield-in-a-chemical-reaction/.
"Topic 6.1: Digestion And Absorption". AMAZING WORLD OF SCIENCE WITH MR.
GREEN, 2020. https://www.mrgscience.com/topic-61-digestion-and-absorption.html.
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