# Lesson Notes By Weeks and Term - Junior Secondary School 2

KINETIC THEORY

TERM: 2nd TERM

SUBJECT: BASIC SCIENCE

CLASS:  JSS 2

REFRENCE

• Precious seed BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOLS BOOK 2

WEEK SIX                                                                                        DATE: ………………..

TOPIC: KINETIC THEORY

Kinetic theory of gases - states  that gases consist of small particles in random motion. The kinetic particle THEORY explains the properties of the different states of matter. The particles in solids, liquids and gases have different amounts of energy. They are arranged differently and move in different ways.

Solids

Property of solids

• They have a fixed shape and cannot flow
• The particles cannot move from place to place
• They cannot be compressed or squashed
• The particles are close together and have no space to move into

Liquids

Property of liquids

• They flow and take the shape of their container
• The particles can move around each other
• They cannot be compressed or squashed
• The particles are close together and have no space to move into

Gases

Gases are made up of molecules. What are molecules? Molecules are the smallest unit which behaves same as the sample, i.e. they have the same chemical properties as of the sample.

Property of gases

• They flow and completely fill their container
• The particles can move quickly in all directions
• They can be compressed or squashed
• The particles are far apart and have space to move into

Changes of state

Melting and freezing

If energy is supplied by heating a solid, the heat energy causes stronger vibrations until the particles eventually have enough energy to break away from the solid arrangement to form a liquid.

When a liquid freezes, the reverse happens. At some temperature, the motion of the particles is slow enough for the forces of attraction to be able to hold the particles as a solid. As the new bonds are formed, heat energy is evolved.

Boiling and condensing

If more heat energy is supplied, the particles eventually move fast enough to break all the attractions between them, and the liquid boils. The heat energy required to convert one  mole of liquid into a gas at its boiling point is called the enthalpy of vaporisation.

If the gas is cooled, at some temperature the gas particles will slow down enough for the attractions to become effective enough to condense it back into a liquid. Again, as those forces are re-established, heat energy is released.

The evaporation of a liquid

The average energy of the particles in a liquid is governed by the temperature. The higher the temperature, the higher the average energy. But within that average, some particles have energies higher than the average, and others have energies lower than the average. Some of the more energetic particles on the surface of the liquid can be moving fast enough to escape from the attractive forces holding the liquid together. They evaporate.

Sublimation

Solids can also lose particles from their surface to form a vapour. Sublimation is the direct change from solid to vapour (or vice versa) without going through the liquid stage.  For example, naphthalene, dry ice of carbon(iv)oxide, Iodine crystals e.t.c

Evaluation

1. State three each of the properties of solid, liquid and gas.
2. What do you understand by enthalpy of vaporization?

Assumptions of kinetic THEORY of gases:

1. All gases are made up of molecules which are constantly and persistently moving in random directions.
2. The separation between the molecules is much greater than the size of molecules.
3. When a gas sample is kept in a container, the molecules of the sample do not exert any force on the walls of the container during collision.
4. The time interval of collision between two molecules, and between a molecule and the wall is considered to be very small.
5. All the collisions between molecules and even between molecules and wall are considered to be elastic.
6. All the molecules in a certain gas sample obey the Newton’s laws of motion.
7. If a gas sample is left for a sufficient time, it eventually comes to a steady state. The density of molecules and the distribution of molecules are independent of position, distance and time.

EVALUATION

1. State four properties of solid, liquid and gas
2. What are the particles of matter?
3. State three assumption of kinetic THEORY of gases.

GENERAL EVALUATION

1. State three each of the properties of solid, liquid and gas.
2. What do you understand by enthalpy of vaporization?
3. State four properties of solid, liquid and gas
4. What are the particles of matter?
5. State three assumption of kinetic THEORY of gases.

WEEKEND ASSIGNMENT

1. All of the following can be compressed except----------- A. oxygen B. hydrogen C. carbon dioxide D. water
2. In which of the following is the kinetic energy of particles of matter is greatest A. gas B. liquid C. solid D. stone
3. The process whereby a substance in solid state changes directly to gaseous state is known as------------ A. freezing B. sublimation C. melting D. cooling
4. Which of these is not a state of matter? A. solid B. water C. liquid D.  gas
5. When a liquid is frozen, it turns to a substance in the------------ form A. gaseous B. solid C. liquid D.  water

THEORY

1. State three assumptions of kinetic THEORY of gases.
2. Differentiate between solid, liquid and gas.