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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

Department of Education ● Republic of the Philippines

i TABLE OF CONTENTS

Page Lesson 1 – Collision Theory and Factors Affecting the Rate of Reaction 3 What’s In 3 What’s New :Effect of Surface Area/Particle Size of the Reactants 4 What is It 5 What’s New:Effect of Concentration on Reaction Rates 6 What is it 7 What’s New:Effect of Temperature on Reaction Rates 7 What is it 8 What’s New: Effect of Catalyst on Reaction Rates 9 What is it 9 What’s More: Identifying Scenarios What’sLearned: True or False) More: Real-life Applications What I Have 10 11 11 Lesson 2 – Limiting Reactants and Percent Yield 12 What I Need to Know 12 What’s In 13

What’s More: Solving Limiting Reactant Problems

15

What’s More: Solving Percent Yield Problems 17 What’s More: Why Percent Yield is Usually Less than 100%? 18 What I Have Learned 18 What I Can Do: Essay 19 Assessment 20 References 23 What’s I Know 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.

2 11. Which of the following substances act as catalysts in the body? A. carbohydrates B. lipidsC. 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 (H2) formed when 25 grams of aluminum reacts with excess hydrochloric acid according to this balanced chemical equation: 35

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2���� +6 ������ → 2��������3 + 3��2 ( ��������: ��; ����; ����; 17 13

A. 0.41 g B. 1.2 g C. 1.8 g D. 2.8 g Lesson

1Collision Theory and the Factors Affecting Reaction Rate

What’s In Chemical reactions are all around us. We witness it every daycombustion, 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. 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 reactant llide effectively, the more often they react wit 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.

3 Factors that Affect Reaction Rates Figure 1. Combustion of LPG Gas- a Figure 2. Rusting of Iron- a chemical chemical reaction with a fast reaction rate. reaction with a slow reaction rate.

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.

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

4 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.

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 Act i vi t y3. 1. 2:EffectofConcent r at i on onReact i onRat es

Table 3.1.2: Effect of Concentration on Reaction Rates Obj ect i ve:t oi nv e st i gat et heeffec tofc onc ent r at i onont her at eofar e ac t i on. Mat er i al s: 2s i mi l arc ups6mLpur eVi neg ar

Guide Questions 1. 5mLofWat er2s poonf ulofBaki ngsoda Pr ocedur e:

1. Which reaction had the fastest rate? Why? 1.I nonec up,usepur evi ne gar( 3mL)andpl ac eones poonf ulofbaki ngs oda. Rec or di nTabl e3. 1. 2

Answer:________________________________________________________ ____________ t het i mei tt akesf ort her e ac t i ont ohappen. _________________________________________________ 2.I nanot he rc up,addpur evi ne gar( 1. 5mL)andwat e r( 1. 5mL)be f or ey ou addt hes poonf ul lofbaki ngsoda.Rec or dr eac t i ont i mei nTabl e3. 1. 2.

2. Concentration

Total Time of Reaction

Observations

Pure Vinegar 50% vinegar + 50% water

1. Explain what could be occurring at the molecular level in each example. (How are the molecules moving or acting?) Answer:____________________________________________________________________

2.Why substances with high concentrations react faster than substances with low concentrations? Answer:____________________________________________________________ ______________

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

5 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 fre quency 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.

Table 3.1.3: The Effect of Temperature on Reaction Rates Temperature of water

Time the tablet was fully dissolved

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:_____________________________________________________

Observations

_______________

What is It

6 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. 4. Effect of a Catalyst on Reaction Rates

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.

Tabl e3. 1. 5Exampl esofEnzymes Enzyme

Produced by

Site of Action

Optimum pH

Digestion

CARBOHYDRATE DIGESTION Salivary amylase

Salivary glands

Mouth

Neutral

Starch+ H2O→maltose

Pancreas

Small Intestine

Basic

Starch+ H2O→maltose

Maltase

Small Intestine

Small Intestine

Basic

Maltose+ H2O→glucose+ glucose

Lactase

Small Intestine

Small Intestine

Basic

Lactose+ H2O→glucose+ galactose

Pepsin

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

Nuclease

Pancreas

Small Intestine

Basic

RNA and DNA +H 2O→nucleotides

Nucleosidases

Small Intestine

Small Intestine

Basic

Nucleotide + H2O→ base+ sugar+phosphate

Pancreas

Small Intestine

Basic

Fat droplet + H2O→ monoglycerides+ fatty acids

Pancreatic amylase

PROTEIN DIGESTION

NUCLEIC ACID DIGESTION

FAT DIGESTION Lipase

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

7 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.

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.

What’s More Activity 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.

What I Have Learned

Factor Affecting Reaction Rate

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.

8 Lesson

2Limiting 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 ...