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.

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