Factors affecting equilibrium and Industrial applications for SS 1

Class: SS 1
Term: Second Term
Week: 10
Age: Approximately 15 years
Duration: 60 minutes
Subject: Chemistry
Curriculum Theme: The chemical world
Focal competence: Identifying reactions in equilibrium
Key competencies/values: Critical Thinking; Communication
Skills:

• Predicting the effects of applied stress (e.g. increased temperature, pressure, concentration, etc.) on systems in equilibrium

Previous Lesson: Chemical Equilibrium and Le Chatelier’s Principle
Topic: Chemical Equilibrium: Factors Affecting Equilibrium (Concentration, Pressure, Temperature, Etc.)
Subject Matter: Factors affecting equilibrium, Industrial applications

Specific Objectives

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

Cognitive Domain

• State Le Chatelier’s Principle.
• Describe the effects of changes in concentration, pressure, and temperature on a system at equilibrium.
• Mention industrial applications of chemical equilibrium.

Affective Domain

• Appreciate the significance of manipulating equilibrium in industrial processes.

Psychomotor Domain

• Predict the direction of equilibrium shift when concentration, pressure, or temperature is altered.

Social Domain

• Collaborate with peers to discuss and explain chemical equilibrium concepts.

Reference Materials

The following resources were used in planning this lesson:

• 2025 New Revised Senior Secondary Education Curriculum (SSEC)
• Relevant State Unified Scheme of Work
• A suitable Chemistry textbook for SS 1
• The HeadTeacher Scheme of work For The New Revised Senior Secondary Education Curriculum (SSEC)

Instructional Materials

The teacher will teach this lesson with the aid of:

• Ice cubes
• Source of heat (e.g., Bunsen burner, hot plate)
• Beakers or transparent containers
• Thermometer
• Charts illustrating reversible reactions and equilibrium shifts
• Chemical equations on a whiteboard or chart
• Whiteboard/Blackboard and markers/chalk

Rationale for the Lesson

This lesson is important for understanding how chemical reactions can be controlled and optimised. It provides students with the foundational knowledge of Le Chatelier’s Principle, which is crucial for predicting and manipulating reaction outcomes. This understanding is directly applicable to various industrial chemical processes, enabling efficient production of essential substances.

Prerequisite/Previous Knowledge

Pupils/students should have prior knowledge of chemical reactions, reversible and irreversible reactions, and basic concepts of reaction rates.

Lesson Content/Board Summary

Chemical Equilibrium: Factors Affecting Equilibrium (Concentration, Pressure, Temperature, Etc.)

Introduction to Chemical Equilibrium

Chemical equilibrium is a state in a reversible chemical reaction where the rate of the forward reaction is equal to the rate of the reverse reaction. At equilibrium, the concentrations of reactants and products remain constant, but the reactions continue to occur in both directions (dynamic equilibrium).

Characteristics of a system at equilibrium:

1. It is dynamic, meaning both forward and reverse reactions are still occurring.
2. The concentrations of reactants and products remain constant over time.
3. It can only be established in a closed system.
4. It can be approached from either direction (starting with reactants or products).

Le Chatelier’s Principle

Le Chatelier’s Principle states that if a change of condition (stress) is applied to a system in equilibrium, the system will shift in a direction that relieves the stress.

The common stresses that can affect a system at equilibrium include changes in concentration, pressure, and temperature.

Factors Affecting Chemical Equilibrium

1. Effect of Concentration Change

If the concentration of a reactant or product is changed, the equilibrium will shift to counteract that change.

1. Increasing the concentration of a reactant: The equilibrium shifts to the right (towards products) to consume the added reactant.
2. Decreasing the concentration of a reactant: The equilibrium shifts to the left (towards reactants) to produce more of the depleted reactant.
3. Increasing the concentration of a product: The equilibrium shifts to the left (towards reactants) to consume the added product.
4. Decreasing the concentration of a product: The equilibrium shifts to the right (towards products) to produce more of the depleted product.

Example: In the reaction (A + B rightleftharpoons C + D)

1. Adding more A or B shifts the equilibrium to the right.
2. Removing C or D shifts the equilibrium to the right.

2. Effect of Pressure Change

Pressure changes primarily affect reactions involving gases. A change in pressure will cause the equilibrium to shift to the side with fewer or more moles of gas to relieve the stress.

1. Increasing the pressure: The equilibrium shifts to the side with fewer moles of gas to reduce the pressure.
2. Decreasing the pressure: The equilibrium shifts to the side with more moles of gas to increase the pressure.

If the number of moles of gas on both sides of the equation is equal, a change in pressure will have no effect on the equilibrium position.

Example: (N_2(g) + 3H_2(g) rightleftharpoons 2NH_3(g))

1. Reactant side has (1+3 = 4) moles of gas.
2. Product side has (2) moles of gas.
3. Increasing pressure shifts equilibrium to the right (fewer moles of gas).
4. Decreasing pressure shifts equilibrium to the left (more moles of gas).

3. Effect of Temperature Change

Temperature changes affect the equilibrium position depending on whether the reaction is exothermic (releases heat) or endothermic (absorbs heat).

1. Increasing the temperature: The equilibrium shifts in the endothermic direction (to absorb the added heat).
2. Decreasing the temperature: The equilibrium shifts in the exothermic direction (to release heat).

Example: (N_2(g) + 3H_2(g) rightleftharpoons 2NH_3(g) quad Delta H = -92 text{ kJ/mol}) (Exothermic forward reaction)

1. Increasing temperature shifts equilibrium to the left (endothermic reverse reaction).
2. Decreasing temperature shifts equilibrium to the right (exothermic forward reaction).

Example: (N_2O_4(g) rightleftharpoons 2NO_2(g) quad Delta H = +58 text{ kJ/mol}) (Endothermic forward reaction)

1. Increasing temperature shifts equilibrium to the right (endothermic forward reaction).
2. Decreasing temperature shifts equilibrium to the left (exothermic reverse reaction).

4. Effect of a Catalyst

A catalyst increases the rate of both the forward and reverse reactions equally. Therefore, a catalyst helps a system reach equilibrium faster but does not change the position of the equilibrium or the concentrations of reactants and products at equilibrium.

Industrial Applications of Chemical Equilibrium

Understanding and applying Le Chatelier’s Principle is vital in optimising industrial chemical processes to maximise product yield.

1. Haber Process (Synthesis of Ammonia):

   (N_2(g) + 3H_2(g) rightleftharpoons 2NH_3(g) quad Delta H = -92 text{ kJ/mol})

   To maximise ammonia yield:

   • High pressure (shifts right, fewer moles of gas).
   • Moderate temperature (a compromise between rate and yield, as low temperature favours yield but slows reaction).
   • Removal of ammonia as it forms (shifts right, decreases product concentration).
   • Use of a catalyst (iron) to speed up the reaction.
2. Contact Process (Manufacture of Sulphuric Acid):

   The key equilibrium step is: (2SO_2(g) + O_2(g) rightleftharpoons 2SO_3(g) quad Delta H = -197 text{ kJ/mol})

   To maximise sulphur trioxide yield:

   • High pressure (shifts right, fewer moles of gas).
   • Moderate temperature (a compromise, as low temperature favours yield but slows reaction).
   • Excess oxygen (shifts right, increases reactant concentration).
   • Use of a catalyst (vanadium(V) oxide, V2O5) to speed up the reaction.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Pair Work

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Demonstration/Questioning

Teacher’s Activity: The teacher introduces the concept of reversible changes by demonstrating the melting and freezing of ice cubes. The teacher places ice cubes in a beaker and asks students what happens when heat is applied and removed. The teacher then asks students to predict what would happen if more ice or more heat was added.

Pupils’ Activity: Pupils observe the demonstration, answer questions, and make predictions about the ice cube experiment.

Learning Point: Reversible changes introduction

Step 2: Chemical Equilibrium Explained

Time: 8 minutes

Teaching Skill: Explanation/Illustration

Teacher’s Activity: The teacher explains what chemical equilibrium is, defining it as a state where forward and reverse reaction rates are equal, leading to constant concentrations. The teacher uses a simple reversible reaction equation on the board to illustrate dynamic equilibrium.

Pupils’ Activity: Pupils listen attentively, ask questions for clarification, and copy the definition and characteristics of chemical equilibrium.

Learning Point: Meaning of chemical equilibrium

Step 3: Le Chatelier’s Principle

Time: 8 minutes

Teaching Skill: Explanation/Definition

Teacher’s Activity: The teacher states Le Chatelier’s Principle clearly and explains its significance in predicting how an equilibrium system responds to stress. The teacher provides simple analogies to make the concept concrete.

Pupils’ Activity: Pupils listen and write down Le Chatelier’s Principle in their notebooks.

Learning Point: Le Chatelier’s Principle statement

Step 4: Effect of Concentration

Time: 8 minutes

Teaching Skill: Guided Discussion/Examples

Teacher’s Activity: The teacher explains how changes in reactant or product concentration affect the equilibrium position. The teacher uses the Haber process equation as an example and guides students to predict the shift when reactant or product concentrations are altered.

Pupils’ Activity: Pupils participate in the discussion, predict equilibrium shifts, and note down the effects of concentration changes.

Learning Point: Concentration effect on equilibrium

Step 5: Effect of Pressure

Time: 8 minutes

Teaching Skill: Explanation/Problem Solving

Teacher’s Activity: The teacher explains the effect of pressure changes on gaseous equilibrium systems, emphasising the role of the number of moles of gas. The teacher uses the Haber process example again, guiding students to determine the shift when pressure is increased or decreased.

Pupils’ Activity: Pupils follow the explanation, work in pairs to discuss the effect of pressure, and record their findings.

Learning Point: Pressure effect on equilibrium

Step 6: Effect of Temperature and Catalyst

Time: 8 minutes

Teaching Skill: Explanation/Comparison

Teacher’s Activity: The teacher explains how temperature changes affect equilibrium, distinguishing between exothermic and endothermic reactions. The teacher also clarifies that a catalyst only speeds up the attainment of equilibrium but does not shift its position.

Pupils’ Activity: Pupils listen, ask questions about temperature effects, and understand the role of catalysts.

Learning Point: Temperature and catalyst effects

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. State Le Chatelier’s Principle.
2. Describe the effect of increasing the concentration of a reactant on an equilibrium system.
3. How does increasing pressure affect the equilibrium of (N_2(g) + 3H_2(g) rightleftharpoons 2NH_3(g))?
4. Mention two industrial applications of chemical equilibrium.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Equilibrium factors understanding

Step 8: Note-Taking

Time: 10 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on chemical equilibrium, Le Chatelier’s Principle, factors affecting equilibrium, and industrial applications into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson content

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Reinforcement

Teacher’s Activity: The teacher summarises the key points of the lesson, reiterating the importance of Le Chatelier’s Principle in predicting equilibrium shifts and its practical applications in industry. The teacher encourages students to review their notes.

Pupils’ Activity: Pupils listen to the summary and ask any final questions.

Learning Point: Lesson concept consolidation

Continuous Assessment/Further Study

Type: Homework/Practice Exercise

Instruction: Answer the following questions in your notebook.

1. For the reaction (PCl_5(g) rightleftharpoons PCl_3(g) + Cl_2(g) quad Delta H = +87.9 text{ kJ/mol}), predict the effect of the following changes on the equilibrium position:
   1. Adding more (PCl_5).
   2. Removing (Cl_2).
   3. Increasing the pressure.
   4. Decreasing the temperature.
2. Research another industrial process (apart from Haber and Contact processes) that applies the principles of chemical equilibrium to maximise product yield. Describe the reaction and the conditions used.

Lesson Keywords

• Chemical equilibrium – A state in a reversible reaction where the rates of forward and reverse reactions are equal.
• Reversible reaction – A reaction that can proceed in both forward and reverse directions.
• Le Chatelier’s Principle – States that a system at equilibrium will shift to relieve any applied stress.
• Concentration – The amount of a substance in a given volume.
• Pressure – Force exerted per unit area, primarily affecting gaseous reactions.
• Temperature – A measure of the average kinetic energy of particles, affecting reaction rates and equilibrium position.
• Catalyst – A substance that speeds up a reaction without being consumed, not affecting equilibrium position.
• Haber process – An industrial process for synthesising ammonia from nitrogen and hydrogen.
• Contact process – An industrial process for manufacturing sulphuric acid.

Differentiation

For students who need additional support, the teacher can provide simplified examples and visual aids for each factor affecting equilibrium. For advanced learners, encourage them to research more complex industrial applications or explore the quantitative aspects of equilibrium constants.

Suggested Lesson Videos

For further understanding of chemical equilibrium and Le Chatelier’s Principle, search on YouTube for:

• “Le Chatelier’s Principle explained SS1 Chemistry”
• “Haber process and Contact process equilibrium”