Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 2nd Term
Week: 7
Age: 15 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemistry
Previous Lesson: Symbols,.
Topic: Gas Laws
Subject Matter: Gay-Lussac’s law, Avogadro’s law, ideal gas equation, and effects of temperature and pressure on gases

Specific Objectives

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

Cognitive Domain:

state Gay-Lussac’s law and write its mathematical form.
state Avogadro’s law and write its mathematical form.
state the ideal gas equation and identify each symbol in the equation.
explain the effect of increase or decrease in temperature on gas volume at constant pressure.
explain the effect of increase or decrease in pressure on gas volume at constant temperature.

Affective Domain:

show carefulness during observations and measurements in gas experiments.
demonstrate a safety-conscious attitude when handling apparatus and heat sources.

Psychomotor Domain:

observe demonstrations with a gas syringe and record changes in volume, temperature, and pressure.
use a thermometer and simple readings from a chart/table to interpret gas-law relationships.
solve simple problems using the ideal gas equation with given values.

work cooperatively in groups to interpret experimental observations and agree on correct statements of the laws.
share results and solutions politely during class review.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum (NERDC).
State Unified Scheme of Work.
Ababio, O. Y. New School Chemistry for Senior Secondary Schools.
OpenStax Chemistry 2e: The Ideal Gas Law (includes pressure–temperature relationship for gases).
Chem LibreTexts: Gas Laws Overview.
CK-12 via LibreTexts: Gay-Lussac’s Law.
CK-12 via LibreTexts: Avogadro’s Law.
Khan Academy: Ideal Gas Equation (PV = nRT).

Instructional Materials

The teacher will teach this lesson with the aid of:

Gas syringes with tight-fitting plungers.
Charts showing P–T, V–T, V–n, and P–V relationships.
Thermometer.
Simple weights/clamps (for applying pressure safely on a gas syringe plunger) or a pressure chart scale.
Warm water bath and cold water bath (bowls) for temperature change demonstration.
Whiteboard/marker or chalkboard/chalk.
Calculator and worksheet for ideal gas equation practice.

Rationale for the Lesson

Gas laws help pupils to understand how gases behave when temperature, pressure, and amount of gas change. This knowledge is important for everyday situations like tyre pressure, gas cylinders, and basic laboratory work in Chemistry.

Prerequisite/Previous Knowledge

Pupils have learned the particle nature of matter, basic properties of gases, and can read simple values from tables and charts.

Lesson Content/Board Summary

GAS LAWS

Gay-Lussac’s Law (Pressure–Temperature Law)

Gay-Lussac’s law states that for a fixed mass of gas at constant volume, the pressure of the gas is directly proportional to its absolute temperature (Kelvin).

The following are the mathematical forms of Gay-Lussac’s law:

P ∝ T (at constant V and n)
P/T = constant
P₁/T₁ = P₂/T₂

Avogadro’s Law (Volume–Amount Law)

Avogadro’s law states that at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles (amount) of the gas.

The following are the mathematical forms of Avogadro’s law:

V ∝ n (at constant T and P)
V/n = constant
V₁/n₁ = V₂/n₂

Ideal Gas Equation

The ideal gas equation relates pressure, volume, temperature, and amount of gas for an ideal gas.

The following are key points of the ideal gas equation:

PV = nRT
P = pressure of the gas
V = volume of the gas
n = number of moles of the gas
T = absolute temperature in Kelvin (K)
R = gas constant (value depends on units used)

Effect of Temperature on Gas Volume

When pressure is constant, changing temperature affects the volume of a gas.

The following are effects of temperature change on gas volume (at constant pressure):

Increase in temperature (in Kelvin) causes increase in gas volume.
Decrease in temperature (in Kelvin) causes decrease in gas volume.
Temperature must be converted to Kelvin before calculations (K = °C + 273).

Effect of Pressure on Gas Volume

When temperature is constant, changing pressure affects the volume of a gas.

The following are effects of pressure change on gas volume (at constant temperature):

Increase in pressure causes decrease in gas volume.
Decrease in pressure causes increase in gas volume.
This relationship is inverse, so P × V is constant for a fixed mass of gas at constant temperature.

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 to mention situations where gas changes occur (tyres on hot days, pumping a bicycle, gas in a syringe). The teacher introduces gas laws and writes the topic on the board.
Pupils’ Activity: Pupils give examples from daily life and listen to the lesson focus.
Learning Point: Gases change in pressure and volume when conditions change.

Step 2: Gay-Lussac’s Law Demonstration and Statement

Time: 8 minutes
Teaching Skill: Demonstration and Explanation
Teacher’s Activity: The teacher demonstrates that heating a fixed volume of gas increases pressure (using a chart/illustration and controlled setup) and explains the pressure–temperature relationship at constant volume. The teacher writes the statement and formula on the board.
Pupils’ Activity: Pupils observe and state the relationship between pressure and temperature for a fixed volume of gas, then copy the law and formula.
Learning Point: At constant volume, pressure increases as temperature increases.

Step 3: Avogadro’s Law Explanation and Examples

Time: 6 minutes
Teaching Skill: Explanation and Questioning
Teacher’s Activity: The teacher explains that adding more moles of gas at constant temperature and pressure increases volume and gives simple examples (inflating a balloon, adding gas into a syringe). The teacher writes the statement and formula on the board.
Pupils’ Activity: Pupils state Avogadro’s law in their own words and copy the formula and examples.
Learning Point: At constant temperature and pressure, volume increases with the amount of gas.

Step 4: Ideal Gas Equation (PV = nRT)

Time: 7 minutes
Teaching Skill: Board Work and Explanation
Teacher’s Activity: The teacher introduces the ideal gas equation, explains each symbol, and shows the need for Kelvin temperature. The teacher solves one sample calculation on the board using simple values.
Pupils’ Activity: Pupils copy the equation, identify the meanings of symbols, convert °C to K in an example, and follow the sample calculation.
Learning Point: Pressure, volume, temperature, and amount of gas are linked by PV = nRT.

Step 5: Demonstration of Temperature Effect on Gas Volume

Time: 7 minutes
Teaching Skill: Demonstration and Observation
Teacher’s Activity: The teacher uses a gas syringe to show volume change when the syringe is placed in warm water and then cold water, keeping pressure as constant as possible. The teacher guides pupils to describe what happens to volume as temperature changes.
Pupils’ Activity: Pupils observe and record changes in volume and state the effect of temperature on volume at constant pressure.
Learning Point: At constant pressure, gas volume increases with increase in temperature.

Step 6: Demonstration of Pressure Effect on Gas Volume

Time: 7 minutes
Teaching Skill: Demonstration and Guided Discovery
Teacher’s Activity: The teacher applies gentle pressure on the gas syringe plunger (or adds small weights) to reduce volume and releases pressure to increase volume, keeping temperature as constant as possible. The teacher guides pupils to state the inverse relationship between pressure and volume.
Pupils’ Activity: Pupils observe and describe how volume changes when pressure increases or decreases, and copy the key points.
Learning Point: At constant temperature, gas volume decreases when pressure increases.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

State Gay-Lussac’s law and write its formula.
State Avogadro’s law and write its formula.
State the ideal gas equation and explain the meaning of P, V, n, and T.
Explain the effect of (a) increased temperature and (b) increased pressure on the volume of a gas.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summary and Reinforcement
Teacher’s Activity: The teacher summarizes Gay-Lussac’s law, Avogadro’s law, the ideal gas equation, and the effects of temperature and pressure on gases. The teacher gives an assignment involving one short ideal gas equation calculation and two theory questions on the laws.
Pupils’ Activity: Pupils copy the summary and assignment and ask questions where necessary.
Learning Point: Gas laws explain and predict gas behaviour under changing conditions.

Lesson Keywords

Gay-Lussac’s law – pressure of a gas is directly proportional to absolute temperature at constant volume.
Avogadro’s law – volume of a gas is directly proportional to the number of moles at constant temperature and pressure.
Ideal gas equation – relationship of gases given by PV = nRT.
Kelvin – absolute temperature scale used in gas-law calculations (K = °C + 273).
Pressure – force per unit area exerted by gas particles on container walls.
Volume – space occupied by a gas.

Differentiation

Pupils who need support will use guided notes with completed formula forms and unit reminders, and will solve simpler substitution questions. Pupils who learn faster will solve additional PV = nRT problems and interpret data from a P–T or V–T table to write correct conclusions.

Note for teachers using this lesson plan

Ensure safe handling of warm water, glassware, and gas syringes, and keep demonstrations simple and visible to the whole class. Emphasize constant conditions for each law and insist on Kelvin temperature for calculations. Provide enough practice questions so pupils can state each law, write the formula, and explain the effects of temperature and pressure clearly.