# CHANGES IN STATES OF MATTER USING KINETIC THEORY

The kinetic theory of matter explains the behavior of matter in terms of the motion of its particles. According to this theory, matter is composed of tiny particles (atoms, molecules, or ions) that are constantly in motion. Changes in states of matter, such as solid to liquid or liquid to gas, can be explained using the kinetic theory. Here’s how it works:

## 1. Solid to Liquid (Melting)

In a solid, the particles are closely packed together and vibrate around fixed positions. When heat is added to the solid, the particles gain kinetic energy, causing them to vibrate more vigorously. Eventually, the particles have enough energy to overcome the attractive forces holding them in fixed positions, and they start to break free and move more freely. This results in the solid melting and transforming into a liquid state.

## 2. Liquid to Gas (Vaporization/Evaporation)

In a liquid, the particles are still close together but have more freedom to move compared to a solid. When heat is added to the liquid, the particles gain more kinetic energy and move faster. At a certain temperature, known as the boiling point, the particles have enough energy to break the intermolecular forces completely. The liquid then undergoes vaporization, where some of the particles at the surface gain enough energy to escape into the gaseous phase. This process is known as evaporation. If the entire liquid boils and turns into a gas rapidly, it is called boiling.

## 3. Gas to Liquid (Condensation)

When a gas loses heat, the particles lose kinetic energy and slow down. As a result, the attractive forces between the particles become more significant. When the gas cools down to a certain temperature, known as the condensation point, the particles lose enough kinetic energy for the intermolecular forces to bring them closer together. This causes the gas to condense and transform into a liquid.

## 4. Liquid to Solid (Freezing/Solidification)

As a liquid loses heat, the particles lose kinetic energy and slow down further. The attractive forces between the particles become strong enough to hold them in fixed positions. At a certain temperature, known as the freezing point, the particles lose enough kinetic energy to form a regular arrangement, resulting in the liquid solidifying and transforming into a solid.

These changes in states of matter occur due to the varying kinetic energy of the particles. Adding or removing heat alters the average kinetic energy of the particles, which in turn affects their motion and arrangement. The kinetic theory provides a useful framework for understanding and explaining these transformations.

## EVAPORATION AND BOILING

### Evaporation

Particles in a liquid are attracted by other neighbouring particles in all directions. When particles with sufficient come near the surface of the liquid, they can break away from the attractive forces of the other nearby molecules and escape into the space above and become vapour or gas. This phenomenon is called evaporation. Evaporation occurs at any temperature, though the rate of evaporation increases with an increase in temperature. Evaporation increases with wind, surface area and lower relative humidity.

### Boiling

When a liquid is heated, the rate of evaporation increases. The vapour pressure of the liquid also increases until a temperature is reached, at which the vapour pressure equals the atmospheric pressure. When this happens, bubbles of vapour form freely in the liquid and rise to the surface. This phenomenon is called boiling. The temperature at which boiling takes place is known as boiling point.

## Factors Affecting Evaporation

### 1. The temperature of the liquid

In a liquid, the particles are in motion. When water is heated, the motion of the particles will become more rapid than before. Each particle that collides with another one will change direction. As the heating continues, the particles will gain more energy.

Some particles will gain sufficient energy to break through the surface tension of the liquid and escape as gas. Evaporation of liquids occur at all temperatures but the rate of evaporation increases with increase in temperature. Since evaporation results in the escape of energetic particles from the liquid body, the average kinetic energy of the liquid is lowered. This results in a drop in temperature of the liquid body. Therefore evaporation results in drop in temperature.

### 2. The nature of the liquid substance

Apart from the temperature, the rate of evaporation is also influenced by the type of liquid. For instance, the rate of evaporation of water is lower than that of petrol.

## EVALUATION

1.The boiling point of pure water is ———-

a.0oC        b.100oC      c.250oC   d.1000oC

2.The movement of solute particles through a medium, from a higher concentration to a lower concentration is called ————–

3.When a liquid is cooled, it ————

1. Condense b. Evaporates c. Freezes   d. Melts   e. Sublimes

SECTION B

1. Explain the following
2. Melting
3. Evaporation
4. Diffusion

2.State the factors affecting Evaporation.

CHANGES IN STATES OF MATTER USING KINETIC THEORY

MOLECULAR STRUCTURES USING KINETIC THEORY

KINETIC ENERGY

FAMILY LIFE EDUCATION

FAMILY LIFE EDUCATION