Basic Science and Technology - Junior Secondary 2 - Boiling and evaporations

TERM: 2^ND TERM

WEEK: 9

CLASS: Junior Secondary School 2

AGE: 13 years

DURATION: 40 minutes each for 2 periods

DATE:

SUBJECT: Basic Science

TOPIC: Boiling and evaporations

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

1. ) Explain boiling and evaporation using kinetic theory
2. ) State and explain the factors that affect evaporation

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

BOILING AND EVAPORATION

Boiling: Boiling is the rapid vaporization of a liquid that occurs when it is heated to its boiling point. According to the kinetic theory of matter, at higher temperatures, the kinetic energy of the particles in the liquid increases. As a result, the particles move more rapidly. When the liquid reaches its boiling point, the particles at the surface gain enough energy to break free from the liquid and turn into gas. The vaporization occurs throughout the entire liquid, not just at the surface, which distinguishes boiling from evaporation.

Evaporation: Evaporation is the process by which molecules at the surface of a liquid escape into the air as gas. This occurs even at temperatures below the boiling point. Kinetic theory explains that at any given temperature, the particles in a liquid are moving at different speeds. Some particles at the surface may have enough kinetic energy to overcome the attractive forces holding them together and escape into the atmosphere. This process is slower than boiling and only happens at the surface of the liquid.

Factors That Affect Evaporation:

• Temperature: As temperature increases, the average kinetic energy of the particles increases. This causes more particles to have enough energy to escape from the liquid, thus increasing the rate of evaporation.
• Surface Area: A larger surface area allows more particles to escape from the liquid. This is why evaporation is faster when a liquid is spread over a larger surface (e.g., a wide shallow dish vs. a tall narrow container).
• Humidity: When the surrounding air has a high humidity (a lot of water vapor), it is harder for the liquid particles to evaporate because the air is already saturated with water molecules. Low humidity speeds up evaporation because there is more room in the air for water molecules to disperse.
• Air Movement (Wind): Wind or air movement helps carry away the water vapor from the surface of the liquid, allowing more particles to escape. This reduces the humidity near the liquid's surface, further accelerating evaporation.
• Nature of the Liquid: Different liquids have different evaporation rates depending on the strength of their intermolecular forces. Liquids with weaker intermolecular forces (e.g., alcohol, acetone) evaporate faster than those with stronger forces (e.g., water)

EVALUATION:

1. What is the difference between boiling and evaporation in terms of molecular movement and energy?
2. How does temperature affect the rate of evaporation, and why?
3. Explain how surface area impacts the evaporation process. Provide an example.
4. What role does humidity play in the rate of evaporation?
5. How does wind or air movement influence the process of evaporation?

CLASSWORK: As in evaluation

CONCLUSION: The teacher marks their books and commends them positively