Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 1st Term
Week: 4
Age: 16 years
Duration: 45 minutes
Subject: Physics
Curriculum Theme: Gas Laws
Previous Lesson: Heat Energy Measurement: Latent Heat, Humidity and Dew Point.
Topic: GAS LAWS
Subject Matter: Meaning of gas laws, measurement of gas pressure, barometers, Boyle’s law, Charles law, pressure law, general gas law.

Specific Objectives

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

Cognitive Domain:

Define gas laws.
Explain how gas pressure is measured.
State the uses of barometers.
State Boyle’s Law, Charles’s Law, Pressure Law, and the General Gas Law.
Solve numerical problems related to gas laws.

Affective Domain:

Appreciate the importance of gas laws in understanding the behavior of gases.
Value accuracy in taking measurements during experiments.

Psychomotor Domain:

Identify different types of barometers.
Observe and record readings from a Boyle’s law apparatus.
Plot and interpret graphs for the relationships between pressure, volume, and temperature.
Apply the gas laws to solve practical problems.

Collaborate with peers during demonstrations and problem-solving activities.
Participate actively in classroom discussions.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Schools Education Curriculum
State Unified Scheme of Work
New School Physics for Senior Secondary Schools by M.W. Anyakoha

Instructional Materials

The teacher will teach this lesson with the aid of:

Physics textbook
Equipped laboratory with Boyle’s law apparatus
Manometer
Mercury barometer
Aneroid barometer
Graph papers
Calculators

Rationale for the Lesson

This lesson helps pupils understand how gases behave under different conditions of pressure, volume, and temperature. Knowledge of gas laws is important for understanding atmospheric phenomena, engine operations, and various industrial processes.

Prerequisite/Previous Knowledge

Pupils have a basic understanding of matter, states of matter, and the concept of pressure from previous lessons.

Lesson Content/Board Summary

GAS LAWS

Meaning of Gas Laws

Gas laws describe the relationships between the measurable properties of gases: pressure (P), volume (V), and absolute temperature (T). These laws help predict how gases will behave under changing conditions.

Measurement of Gas Pressure

Gas pressure is the force exerted by gas particles on the walls of their container. It can be measured using:

Manometer: A device used to measure the pressure of a gas in a container relative to atmospheric pressure. It typically consists of a U-shaped tube containing a liquid (e.g., mercury or water).
Units of Pressure: Common units include Pascal (Pa), atmospheres (atm), millimeters of mercury (mmHg), and torr.

Barometers

Barometers are instruments used to measure atmospheric pressure.

Mercury Barometer: Consists of an inverted tube of mercury in a dish of mercury. The height of the mercury column indicates atmospheric pressure.
Aneroid Barometer: A metal box with a flexible lid, from which air has been removed. Changes in atmospheric pressure cause the lid to expand or contract, which moves a pointer on a scale.
Uses of Barometers: Weather forecasting, determining altitude.

Boyle’s Law

Boyle’s Law states that for a fixed mass of gas at constant temperature, the volume of the gas is inversely proportional to its pressure.

Formula: P ∝ 1/V or PV = k (constant)

For two different states of the same gas at constant temperature:

P₁V₁ = P₂V₂

P₁ = Initial pressure
V₁ = Initial volume
P₂ = Final pressure
V₂ = Final volume

Graph: A graph of P against V gives a curve (hyperbola). A graph of P against 1/V gives a straight line passing through the origin.

Example 1: A gas occupies a volume of 500 cm³ at a pressure of 1.5 atm. If the pressure is increased to 2.5 atm at constant temperature, what will be the new volume?

Solution:
Step 1: Identify given values.
P₁ = 1.5 atm, V₁ = 500 cm³
P₂ = 2.5 atm, V₂ = ?

Step 2: State Boyle’s Law formula.
P₁V₁ = P₂V₂

Step 3: Substitute values into the formula.
(1.5 atm) × (500 cm³) = (2.5 atm) × V₂

Step 4: Solve for V₂.
V₂ = (1.5 × 500) / 2.5
V₂ = 750 / 2.5
V₂ = 300 cm³

The new volume will be 300 cm³.

Charles’s Law

Charles’s Law states that for a fixed mass of gas at constant pressure, the volume of the gas is directly proportional to its absolute temperature.

Formula: V ∝ T or V/T = k (constant)

For two different states of the same gas at constant pressure:

V₁/T₁ = V₂/T₂

V₁ = Initial volume
T₁ = Initial absolute temperature (in Kelvin)
V₂ = Final volume
T₂ = Final absolute temperature (in Kelvin)

NOTE: Always convert temperature from Celsius (°C) to Kelvin (K) by adding 273 (T(K) = T(°C) + 273).

Graph: A graph of V against T (in Kelvin) gives a straight line passing through the origin.

Example 2: A gas has a volume of 200 cm³ at 27 °C. What will be its volume at 77 °C if the pressure remains constant?

Solution:
Step 1: Convert temperatures to Kelvin.
T₁ = 27 °C + 273 = 300 K
T₂ = 77 °C + 273 = 350 K

Step 2: Identify given values.
V₁ = 200 cm³, T₁ = 300 K
V₂ = ?, T₂ = 350 K

Step 3: State Charles’s Law formula.
V₁/T₁ = V₂/T₂

Step 4: Substitute values into the formula.
200 / 300 = V₂ / 350

Step 5: Solve for V₂.
V₂ = (200 × 350) / 300
V₂ = 70000 / 300
V₂ = 233.33 cm³

The new volume will be approximately 233.33 cm³.

Pressure Law (Gay-Lussac’s Law)

The Pressure Law states that for a fixed mass of gas at constant volume, the pressure of the gas is directly proportional to its absolute temperature.

Formula: P ∝ T or P/T = k (constant)

For two different states of the same gas at constant volume:

P₁/T₁ = P₂/T₂

P₁ = Initial pressure
T₁ = Initial absolute temperature (in Kelvin)
P₂ = Final pressure
T₂ = Final absolute temperature (in Kelvin)

Graph: A graph of P against T (in Kelvin) gives a straight line passing through the origin.

General Gas Law (Combined Gas Law)

The General Gas Law combines Boyle’s, Charles’s, and Pressure Laws into a single equation. It states that for a fixed mass of gas, the ratio of the product of pressure and volume to its absolute temperature is constant.

Formula: PV/T = k (constant)

For two different states of the same gas:

P₁V₁/T₁ = P₂V₂/T₂

P₁ = Initial pressure
V₁ = Initial volume
T₁ = Initial absolute temperature (in Kelvin)
P₂ = Final pressure
V₂ = Final volume
T₂ = Final absolute temperature (in Kelvin)

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 introduces the topic “Gas Laws” by asking pupils about their experiences with gases, e.g., how a balloon expands when heated or contracts when cooled, or how a tyre can burst if over-inflated. The teacher then explains that these observations relate to the behavior of gases.
Pupils’ Activity: Pupils share their experiences and listen attentively to the teacher’s introduction.
Learning Point: Pupils are introduced to the concept of gas behavior and its relevance.

Step 2: Measurement of Gas Pressure and Barometers

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains what gas pressure is, its units, and how it is measured using a manometer. The teacher also shows different types of barometers (mercury and aneroid) and explains their construction, working principle, and practical uses.
Pupils’ Activity: Pupils observe the manometers and barometers, identify their parts, and note their uses.
Learning Point: Pupils understand how gas pressure is measured and the function of barometers.

Step 3: Boyle’s Law Demonstration

Time: 10 minutes
Teaching Skill: Demonstration/Observation
Teacher’s Activity: The teacher demonstrates Boyle’s law using a Boyle’s law apparatus. The teacher guides pupils to record corresponding pressure and volume readings as the volume is changed, ensuring temperature is kept constant.
Pupils’ Activity: Pupils observe the demonstration, record the readings in their notebooks, and discuss the observed relationship between pressure and volume.
Learning Point: Pupils observe the inverse relationship between pressure and volume for a gas at constant temperature.

Step 4: Explanation of Boyle’s Law and Problem Solving

Time: 5 minutes
Teaching Skill: Explanation/Problem Solving
Teacher’s Activity: The teacher explains Boyle’s Law, its formula, and how to plot its graph (P vs V and P vs 1/V). The teacher then solves a worked example on Boyle’s Law on the board.
Pupils’ Activity: Pupils copy the notes and the worked example, paying attention to the steps involved in solving the problem.
Learning Point: Pupils understand the mathematical representation of Boyle’s Law and can solve related problems.

Step 5: Charles’s Law

Time: 5 minutes
Teaching Skill: Explanation/Problem Solving
Teacher’s Activity: The teacher explains Charles’s Law, its formula (emphasizing the use of absolute temperature in Kelvin), and how to plot its graph (V vs T). The teacher solves a worked example on Charles’s Law on the board.
Pupils’ Activity: Pupils listen, take notes, and copy the worked example, ensuring they understand the temperature conversion to Kelvin.
Learning Point: Pupils understand the direct relationship between volume and absolute temperature and can solve related problems.

Step 6: Pressure Law and General Gas Law

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the Pressure Law (Gay-Lussac’s Law) and its formula, and then introduces the General Gas Law (Combined Gas Law) as a combination of Boyle’s, Charles’s, and Pressure Laws, presenting its formula.
Pupils’ Activity: Pupils listen and copy the formulas and definitions for the Pressure Law and the General Gas Law.
Learning Point: Pupils understand the relationships described by the Pressure Law and the combined General Gas Law.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define Gas Laws.
Name two instruments used to measure gas pressure.
State Boyle’s Law.
A gas occupies 600 cm³ at 1.2 atm. What will be its volume if the pressure is reduced to 0.8 atm at constant temperature?
State Charles’s Law and explain why temperature must be in Kelvin.
A gas has a volume of 300 cm³ at 0 °C. What is its volume at 50 °C if the pressure is constant?

Pupils’ Activity: Pupils answer orally and in writing.
Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the definitions and formulas of Boyle’s, Charles’s, Pressure, and General Gas Laws. The teacher also assigns homework related to solving more problems on gas laws.
Pupils’ Activity: Pupils listen to the summary and copy the assigned homework.
Learning Point: Pupils consolidate their understanding of gas laws.

Lesson Keywords

Pressure – The force exerted per unit area.
Volume – The amount of space occupied by a gas.
Temperature – A measure of the average kinetic energy of gas particles.
Boyle’s Law – Relates pressure and volume (inverse relationship).
Charles’s Law – Relates volume and absolute temperature (direct relationship).
Manometer – An instrument for measuring gas pressure.
Barometer – An instrument for measuring atmospheric pressure.
General Gas Law – Combines Boyle’s, Charles’s, and Pressure Laws.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide more complex numerical problems or ask them to research real-world applications of gas laws. For those who need more support, the teacher will provide additional guided practice, simplify explanations, and focus on basic definitions and formulas.

Note for teachers using this lesson plan

Ensure all safety precautions are followed during the Boyle’s Law demonstration. Emphasize the importance of converting temperature to Kelvin for Charles’s Law, Pressure Law, and the General Gas Law. Encourage pupils to draw and interpret graphs as this skill is essential in physics.