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:
- Explain how temperature affects evaporation.
- Explain diffusion using kinetic theory.
- Define evaporation.
- 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:
- Solid
- Liquid
- Gas
Change of state occurs due to temperature changes.
Heating Processes
- Melting (Solid to Liquid)
- Heat increases kinetic energy of particles.
- Particles break free from fixed positions and move.
- Boiling (Liquid to Gas)
- Particles gain enough energy to escape as vapor.
- Evaporation (Liquid to Gas at Any Temperature)
- Even below boiling point, some particles escape as vapor.
Cooling Processes
- Condensation (Gas to Liquid)
- As gas cools, particles lose energy and move closer together.
- 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
- The pressure of a gas is caused by ____.
a) Energy
b) Power
c) Force
d) Work
Answer: c) Force - Only the fastest-moving molecules can overcome ____.
a) Work
b) Power
c) Intermolecular forces
d) Temperature
Answer: c) Intermolecular forces - ____ can occur at any temperature.
a) Evaporation
b) Boiling
c) Melting
d) Condensation
Answer: a) Evaporation - As the speed of molecules increases, pressure ____.
a) Decreases
b) Increases
c) Stops
d) Remains constant
Answer: b) Increases - 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
- Why does evaporation occur?
- How does the kinetic theory explain diffusion?
- Why is energy required to evaporate a liquid?
- How does the surface area of a liquid affect evaporation?
- How does temperature affect evaporation?
- Explain why a gas exerts pressure on the walls of its container.
- What happens when a gas is heated in a fixed volume container?
- How does a gas behave when compressed at constant temperature?
- What is the relationship between temperature and the kinetic energy of particles?
- Explain how condensation occurs.
Conclusion
- The teacher summarizes the lesson and ensures students copy the correct notes.
- Corrections are made where necessary.
Assignment
- Explain how a gas exerts pressure on its container.
- Differentiate between boiling and evaporation.
- List and explain three types of phase changes.
