Explanation of Some Phenomena Using Kinetic Theory & Changes in the States of Matter

Basic Science Lesson Note for JSS 2 (Basic 8)

Second Term – Week 7

Topic: Explanation of Some Phenomena Using Kinetic Theory & Changes in the States of Matter

Instructional Materials

• Gas cylinder
• Bunsen burner
• Kettle for boiling water
• Pictures of objects in solid, liquid, and gaseous states

Reference Materials

• Scheme of Work
• Online Information
• Textbooks
• Workbooks
• 9-Year Basic Education Curriculum

Previous Knowledge

Students have been taught the Kinetic Theory in their previous lesson.

Behavioral Objectives

At the end of the lesson, learners should be able to:

1. Explain how temperature affects evaporation.
2. Explain diffusion using kinetic theory.
3. Define evaporation.
4. State how gas exerts pressure on the walls of its container.

Content

How Does a Gas Exert Pressure on the Walls of Its Container?

• Gas particles are in constant motion and collide with the walls of the container.
• These collisions create force, and the force per unit area is known as gas pressure.

Why Is Energy Required to Evaporate a Liquid?

• In a liquid, molecules are held together by intermolecular forces.
• Only the fastest-moving molecules can overcome these forces and escape as vapor.
• Energy is required to break these attractive forces, which leads to evaporation.

Why Does Evaporation Occur?

• In a liquid, molecules constantly collide.
• Some molecules at the surface gain enough kinetic energy to break free from the liquid.
• This process leads to evaporation, which can occur at any temperature.

Why Does Cooling Occur When a Liquid Evaporates?

• The molecules with the most energy leave the liquid first.
• This reduces the average kinetic energy of the remaining molecules.
• Since temperature is directly related to kinetic energy, the temperature drops, causing cooling.

Why Does a Liquid Evaporate Faster in a Draught?

• In moving air, evaporated molecules are quickly carried away.
• More molecules escape from the surface, leading to faster evaporation.

How Does the Surface Area of a Liquid Affect Evaporation?

• Evaporation happens at the surface of a liquid.
• A larger surface area means more molecules can escape, increasing the rate of evaporation.

How Does Temperature Affect Evaporation?

• Higher temperatures give molecules more energy to escape from the liquid.
• This increases the rate of evaporation.

Gas Behavior in Different Conditions

1. Heating a Fixed Mass of Gas in a Container with Fixed Volume

• When the gas is heated, molecules move faster.
• Faster molecules collide more frequently with the container walls.
• This increases pressure (Pressure increases as Temperature increases).

2. Heating a Fixed Mass of Gas in a Container with Fixed Pressure

• If pressure remains the same, the volume of the gas must increase to accommodate faster-moving molecules.
• (Volume increases as Temperature increases).

3. Compressing a Gas at a Fixed Temperature (Boyle’s Law)

• At constant temperature, gas molecules move at the same speed.
• Reducing the volume increases collisions, causing the pressure to increase.
• (Pressure increases as Volume decreases).

Kinetic Theory and Diffusion

• Diffusion occurs because molecules are in constant motion.
• Molecules move from areas of higher concentration to lower concentration.
• Gas molecules diffuse faster than liquids due to weak intermolecular forces.

Change of State and Kinetic Theory

A substance can exist in three states:

1. Solid
2. Liquid
3. Gas

Change of state occurs due to temperature changes.

Heating Processes

1. Melting (Solid to Liquid)
   • Heat increases kinetic energy of particles.
   • Particles break free from fixed positions and move.
2. Boiling (Liquid to Gas)
   • Particles gain enough energy to escape as vapor.
3. Evaporation (Liquid to Gas at Any Temperature)
   • Even below boiling point, some particles escape as vapor.

Cooling Processes

1. Condensation (Gas to Liquid)
   • As gas cools, particles lose energy and move closer together.
2. Freezing (Liquid to Solid)
   • Further cooling causes particles to settle into fixed positions.

Presentation

Step 1:

• The teacher revises the previous lesson.

Step 2:

• The teacher introduces the new topic and explains key concepts.

Step 3:

• The teacher allows students to give their own examples and corrects their mistakes.

Evaluation Questions

Multiple Choice Questions

1. The pressure of a gas is caused by ____.
   a) Energy
   b) Power
   c) Force
   d) Work
   Answer: c) Force
2. Only the fastest-moving molecules can overcome ____.
   a) Work
   b) Power
   c) Intermolecular forces
   d) Temperature
   Answer: c) Intermolecular forces
3. ____ can occur at any temperature.
   a) Evaporation
   b) Boiling
   c) Melting
   d) Condensation
   Answer: a) Evaporation
4. As the speed of molecules increases, pressure ____.
   a) Decreases
   b) Increases
   c) Stops
   d) Remains constant
   Answer: b) Increases
5. According to Boyle’s Law, pressure ____.
   a) Decreases when volume increases
   b) Increases when volume increases
   c) Remains the same
   d) Doubles as volume increases
   Answer: a) Decreases when volume increases

Theory Questions

1. Why does evaporation occur?
2. How does the kinetic theory explain diffusion?
3. Why is energy required to evaporate a liquid?
4. How does the surface area of a liquid affect evaporation?
5. How does temperature affect evaporation?
6. Explain why a gas exerts pressure on the walls of its container.
7. What happens when a gas is heated in a fixed volume container?
8. How does a gas behave when compressed at constant temperature?
9. What is the relationship between temperature and the kinetic energy of particles?
10. Explain how condensation occurs.

Conclusion

• The teacher summarizes the lesson and ensures students copy the correct notes.
• Corrections are made where necessary.

Assignment

1. Explain how a gas exerts pressure on its container.
2. Differentiate between boiling and evaporation.
3. List and explain three types of phase changes.