Unit Five: Physical States of Matter

Lesson 1: Properties of Gases and the kinetic molecular theory of gases

Comptencies
Starter Activities
Main Activites

Competencies

Explain properties of gases
Give the kinetic molecular theory explanation for the properties of gases
Give examples of the properties of gases

Materials

Charts for arrangements of the different physical states of substances, balloons, syringes,

Note for the teacher

The difference between the three physical states of matter is the type of interactions among their particles. These interactions depend on the intra-molecular and intermolecular attractive forces students investigated sofar in unit three. The important point in the study of gases is identifying the properties and their kinetic molecular theory explanations. Students usually have difficulty of understanding that most of the space in the gases is empty. So, they should be able to explain, describe and give kinetic molecular theory explanations of the properties of gases.

Starter activity (6 minutes)

This lesson can be started by reviewing the kinetic theory of matter. Let the students discuss the kinetic theory of matter.

Procedure

Make the students in groups depending on your class size
Let them discuss the three assumptions of the kinetic theory of matter
Instruct them to use small sphere drawing to represent molecules of substances
They should use pencil and paper to describe their understanding of properties of gases, liquids and solids under the same conditions.
Let the group representatives present their findings of the difference between the three physical states.

This presentation will create a good opportunity to know the students’ conceptualization of the kinetic theory of matter.. Questions and answers should be encouraged during the discussion and presentation.

Students may come up with different views and drawings. However, you may use the correct explanation and drawings to harmonize their ideas.

The following points may be highlighted to explain the assumptions

Particles of matter can be atoms, ions or molecules. These particles are moving continuously; the gas particles move randomly colliding with other molecules and with the wall of their container. Liquids are neither as random as gases nor as restricted as solids. Particles of liquids can roll over one another and mix up. The solids are restricted to vibrating to their mean positions.
The motions and positions of the particles of matter make them to have kinetic and potential energies.
The gas particles are more energetic than liquid particles and liquids particles are more energetic than solid particles.

Evaluation

Students may be asked to point out the differences between gas, liquid and solid states based on the explanation of the kinetic molecular theory.

Main activity (25 minutes)

Discussing and giving explanation on properties of gases

Procedure

Let the students continue the starter activity in groups
Provide them balloons, syringes, balances
Read properties of gases on your text book page 168 and the kinetic molecular theory on pages 170 and 171.
Explain properties of gases giving by kinetic molecular theory explanation.
Use different materials as examples to describe and demonstrate your explanation
Report your findings in tabular form as follows

Property of a gas	Kinetic molecular theory explanation	Description examples

Let the group representatives present their discussion points and demonstrations in group. As usual discussions should be encouraged. Finally they should come to the consensus like the following

Property of a gas	Kinetic molecular theory explanation	Description examples
Gases have no definite shape and definite volume	Assumption 1 The particles are in the state of constant, rapid and random motions	They may blow balloons of different shape and size and show the effect
Gases can easily compressed	Assumption 2 The space between the particles of gases are very far	They may sack gas with syringe, close the mouth of the syringe with their finger and try to compress
Gases have low densities compared with liquids and solids	Assumption 2 As density is mass per unit volume, gases have low density because they have small number of particles in relatively large space of volume	They may measure mass of a balloon full of gas and some millilitres of water in the similar balloon.
Gases exert pressure in all directions	Assumption 1 Gases collide with wall of their container continuously in all direction. This collision exerts pressure on their container.	They may blow the balloon and see that it inflates in all directions.
Gases easily flow and diffuse through one another	Assumption 3 and 5 No attraction force between particles, their kinetic energy depend on their temperature	They may release the mouth of the balloon they blown to see gas flowing out.

Evaluation

Procedure

Each student should have three small cards of green, yellow and red colours. It can be made up of Manila paper or old document folders.
You would state the properties of gases and their explanation one after the other.
Students raise their cards in response; the green for agree, the yellow if they are not sure and red if they didn’t understand the idea at all.

This helps you to know how much of the students have internalized the lesson. Then you can invite students with green cards to explain for those with red cards. Finally you may correct students’ responses if necessary.

Concluding activity (5 minutes)

Let students discuss applications of gas in daily life.
They may mention points like:

Air fills into the tyre of vehicles and exerts pressure
Light gases are filled into balloons for scientific researches and recreations etc.

Lesson that can be taught by similar methods are:

Properties of liquids
Properties of solids