Basic Science and Technology - Junior Secondary 2 - Explanation of some phenomena using kinetic energy

TERM: 2^ND TERM

WEEK: 8

CLASS: Junior Secondary School 2

AGE: 13 years

DURATION: 40 minutes each for 2 periods

DATE:

SUBJECT: Basic Science

TOPIC: Explanation of some phenomena using the Kinetic theory

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

1. ) Explain some phenomena using the kinetic theory

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, story-telling, videos from source

INSTRUCTIONAL MATERIALS: Recommended Basic Science textbooks for Junior Secondary School 2

INSTRUCTIONAL PROCEDURES: PERIOD 1-2:

NOTE

EXPLANATION OF SOME PHENOMENA USING THE KINETIC THEORY

(i) The Behaviors of Solids, Liquids, and Gases under Different Temperatures and Pressures:

• Solids: In solids, particles are closely packed and vibrate in place, with very little movement. As the temperature increases, the particles gain kinetic energy and vibrate more vigorously. When the temperature becomes high enough (e.g., melting point), the solid may turn into a liquid (melting), as the particles have enough energy to break free from their fixed positions.
• Liquids: In liquids, the particles are still close together but can move past each other. As temperature increases, the particles gain more kinetic energy, causing the liquid to expand. If the temperature reaches the boiling point, the liquid may turn into a gas as the particles gain enough energy to overcome the intermolecular forces holding them together.
• Gases: Gas particles are far apart and move freely at high speeds. As the temperature increases, the particles move even faster, and the gas expands. When pressure increases, the gas particles are compressed, reducing the volume as they are forced closer together.

(ii) The Large Increase in the Volume of a Liquid (e.g., 1 cm³) when Converted to Vapour:

When a liquid is converted to vapor (evaporates), the particles gain enough energy to break the intermolecular forces that hold them together. In the liquid state, particles are closely packed, but in the gaseous state, they move freely and are much farther apart. This increase in the distance between particles leads to a dramatic increase in volume. For example, water expands approximately 1600 times in volume when it changes from liquid to steam (vapor).

(iii) Why There is Only a Small Amount of Hydrogen or Helium in Earth’s Atmosphere Compared to Jupiter’s:

Hydrogen and helium are lighter gases with low molecular masses. The Earth's atmosphere is held by gravity, but because of their low molecular masses, these gases move at high velocities, which can exceed the Earth's escape velocity (the speed at which particles must move to escape the gravitational pull). As a result, hydrogen and helium atoms can escape the Earth's atmosphere over time, leading to their lower concentrations. On Jupiter, the stronger gravity and colder temperatures help retain these gases, allowing them to accumulate in larger amounts.

(iv) Why Substances Can Exist as Solid, Liquid, or Gas:

The state in which a substance exists depends on the temperature and pressure, which affect the kinetic energy of the particles.

• In a solid, the particles have low kinetic energy, are closely packed, and vibrate in fixed positions.
• In a liquid, the particles have enough kinetic energy to move past each other, but they are still closely packed, allowing the liquid to flow.
• In a gas, the particles have high kinetic energy and move freely, allowing gases to expand and fill their containers.

The transition between these states (e.g., melting, freezing, boiling, condensation) occurs when the temperature or pressure changes enough to alter the kinetic energy of the particles.

(v) Why a Solid Has Shape While Liquid and Gas Have None:

• Solids: In solids, particles are arranged in a regular, fixed pattern with strong intermolecular forces. These forces keep the particles in place, giving the solid a definite shape.
• Liquids: In liquids, the intermolecular forces are weaker than in solids, allowing particles to move past each other. While the particles are still close together, the liquid takes the shape of its container but does not have a fixed shape.
• Gases: In gases, the particles are far apart and move freely at high speeds. The intermolecular forces are so weak that gas particles do not stay in any fixed shape and will expand to fill any container.

EVALUATION:

1. How does the kinetic energy of particles in a substance change with temperature, and how does this affect the state of matter (solid, liquid, gas)?
2. Explain why the volume of a liquid increases drastically when it is converted to vapor, using the kinetic theory of matter.
3. Using the kinetic theory, explain why Earth has a small amount of hydrogen and helium compared to Jupiter.
4. Why do substances exist in different states of matter (solid, liquid, gas) and how do temperature and pressure influence this?
5. Describe the kinetic theory's explanation for why solids have a definite shape, while liquids and gases do not.

CLASSWORK: As in evaluation

CONCLUSION: The teacher marks their books and commends them positively