Lesson Note on Chemical Reactions: Meaning, Reactants, Products and Collision Theory for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: First Term
Week: 4
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemical Reactions
Previous Lesson: Periodic Table: Trends, Diagonal Relationship and Ionization Energy.
Topic: CHEMICAL REACTIONS
Subject Matter: Meaning of chemical reactions (process where reactants change to products), reactants, products, reaction time, reaction rate, introduction to collision theory

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

• Define a chemical reaction.
• Identify reactants and products in a given chemical reaction.
• Explain the concepts of reaction time and reaction rate.
• State the factors that affect the rate of a chemical reaction.
• Describe the basic principles of collision theory.

Affective Domain:

• Appreciate the importance of chemical reactions in everyday life.
• Show interest in observing chemical changes during experiments.

Psychomotor Domain:

• Write simple word equations for chemical reactions.
• Observe and describe changes in reaction speed during simple demonstrations.

Social Domain:

• Work collaboratively with peers during experimental observations and discussions.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• New School Chemistry for Senior Secondary Schools

Instructional Materials

The teacher will teach this lesson with the aid of:

• Hydrochloric acid (HCl)
• Copper(II) sulfate (CuSO4)
• Sodium chloride (NaCl)
• Ammonium hydroxide (NH4OH)
• Ammonium chloride (NH4Cl)
• Source of heat (Bunsen burner)
• Water
• Test tubes
• Beakers
• Mortar and pestle
• Stopwatch

Rationale for the Lesson

This lesson helps pupils understand how substances change into new ones and the factors that influence how quickly these changes occur. It provides a foundation for understanding many chemical processes around them, from cooking to industrial production.

Prerequisite/Previous Knowledge

Pupils are expected to have a basic understanding of elements, compounds, mixtures, and the differences between physical and chemical changes from their junior secondary school science classes.

Lesson Content/Board Summary

CHEMICAL REACTIONS

Meaning of Chemical Reactions

A chemical reaction is a process that involves the rearrangement of the molecular or ionic structure of a substance, as opposed to a change in physical form or a nuclear reaction. In a chemical reaction, reactants are transformed into products.

Reactants and Products

In any chemical reaction:

• Reactants: These are the starting materials that undergo change during a chemical reaction. They are typically written on the left side of a chemical equation.
• Products: These are the new substances formed as a result of the chemical reaction. They are typically written on the right side of a chemical equation.

Example:

Hydrogen + Oxygen → Water

• Reactants: Hydrogen, Oxygen
• Product: Water

Example:

Calcium Carbonate (solid) + Hydrochloric Acid (aqueous) → Calcium Chloride (aqueous) + Water (liquid) + Carbon Dioxide (gas)

• Reactants: Calcium Carbonate, Hydrochloric Acid
• Products: Calcium Chloride, Water, Carbon Dioxide

Reaction Time and Reaction Rate

• Reaction Time: This is the duration it takes for a chemical reaction to go to completion or for a specific amount of product to be formed.
• Reaction Rate: This refers to how fast or slow a chemical reaction proceeds. It is defined as the change in concentration of a reactant or product per unit time. A fast reaction has a high rate, while a slow reaction has a low rate.

Introduction to Collision Theory

Collision theory explains how chemical reactions occur and why reaction rates differ. It states that for a reaction to occur, reactant particles (atoms, ions, or molecules) must collide with each other.

For a collision to be effective and lead to a reaction, two conditions must be met:

• Proper Orientation: The colliding particles must be correctly oriented for the bonds to break and new bonds to form.
• Sufficient Energy (Activation Energy): The colliding particles must possess a minimum amount of kinetic energy, known as activation energy, to overcome the energy barrier and initiate the reaction.

Factors Affecting the Rate of Chemical Reactions

The rate at which a chemical reaction occurs can be influenced by several factors:

• Temperature: Increasing the temperature generally increases the reaction rate because particles gain more kinetic energy, leading to more frequent and more energetic collisions.
• Concentration: For reactants in solution or gas phase, increasing their concentration increases the number of particles per unit volume, leading to more frequent collisions and thus a faster reaction rate.
• Surface Area: For solid reactants, increasing the surface area (e.g., by crushing a lump into powder) exposes more particles to react, increasing the collision frequency and reaction rate.
• Pressure: For gaseous reactants, increasing the pressure increases the concentration of gas particles, leading to more frequent collisions and a faster reaction rate.
• Catalyst: A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. It does this by providing an alternative reaction pathway with lower activation energy.
• Nature of Reactants: Different substances react at different rates due to their inherent chemical properties, bond strengths, and electron configurations.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher asks pupils about everyday observations of changes in substances, like rusting of iron or burning of wood, to link to chemical reactions. The teacher then introduces the topic: Chemical Reactions.
Pupils’ Activity: Pupils respond to the questions and listen attentively to the introduction of the topic.
Learning Point: Pupils recall prior knowledge and connect it to the new topic.

Step 2: Meaning of Chemical Reactions

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines chemical reactions as processes where reactants change into products, using simple word equations like hydrogen + oxygen → water. The teacher distinguishes between reactants and products.
Pupils’ Activity: Pupils listen, take notes, and identify reactants and products in the examples given.
Learning Point: Pupils understand the definition of a chemical reaction, reactants, and products.

Step 3: Reaction Time and Reaction Rate

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains reaction time and reaction rate. The teacher demonstrates a fast reaction (e.g., reaction of magnesium ribbon with dilute HCl) and a slower reaction (e.g., rusting of iron discussed orally) to illustrate the concept of reaction speed.
Pupils’ Activity: Pupils observe the demonstration, listen to the explanation, and note the differences in reaction speeds.
Learning Point: Pupils grasp the concepts of reaction time and reaction rate through examples.

Step 4: Introduction to Collision Theory

Time: 7 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher introduces the basic concept of collision theory, explaining that particles must collide with sufficient energy and proper orientation for a reaction to occur. The teacher uses simple analogies to explain effective collisions.
Pupils’ Activity: Pupils listen and ask questions for clarification regarding collision theory.
Learning Point: Pupils understand the fundamental requirements for a chemical reaction according to collision theory.

Step 5: Factors Affecting Reaction Rate

Time: 8 minutes
Teaching Skill: Discussion/Explanation
Teacher’s Activity: The teacher discusses various factors affecting reaction rates, such as temperature, concentration, surface area, pressure, catalysts, and the nature of reactants. The teacher provides practical examples for each factor.
Pupils’ Activity: Pupils contribute to the discussion by recalling relevant examples and taking notes.
Learning Point: Pupils learn about the different factors that can influence how fast a chemical reaction proceeds.

Step 6: Practical Observation of Factors

Time: 5 minutes
Teaching Skill: Demonstration/Observation
Teacher’s Activity: The teacher conducts a simple experiment to show the effect of surface area (e.g., comparing the reaction of powdered marble chips vs. lump marble chips with dilute HCl) or temperature (e.g., dissolving sugar in hot vs. cold water).
Pupils’ Activity: Pupils observe the experiment carefully and describe the changes in reaction speed based on the factor being varied.
Learning Point: Pupils gain practical insight into how factors affect reaction rates.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Define a chemical reaction.
2. Distinguish between reactants and products, giving one example.
3. What is reaction rate?
4. State any three factors that affect the rate of a chemical reaction.
5. Briefly explain what collision theory states about chemical reactions.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, emphasizing the importance of understanding chemical reactions and their rates. The teacher then assigns homework.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils reinforce their understanding and prepare for further study.

Lesson Keywords

• Chemical reaction – A process that transforms one or more substances into different substances.
• Reactants – The starting substances in a chemical reaction.
• Products – The new substances formed in a chemical reaction.
• Reaction rate – The speed at which a chemical reaction proceeds.
• Collision theory – A theory explaining reaction rates based on the collision of reacting particles.
• Activation energy – The minimum energy required for a chemical reaction to occur.
• Catalyst – A substance that speeds up a reaction without being consumed.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research specific industrial applications of reaction rate control. For those needing more support, the teacher can provide simplified diagrams of collision theory and more guided examples of identifying reactants and products.

Note for teachers using this lesson plan

Ensure all necessary instructional materials are prepared before the lesson. Emphasize safety precautions during demonstrations, especially when using acids and heat sources. Encourage pupils to relate the concepts to everyday phenomena to make learning more engaging and relevant.