# NATURE OF MATTER

Matter is anything that has weight and occupies space. It exists in three states namely: solid, liquid and gas. The fundamental difference between the three states of matter depends on the degree of movement of the particles they are made of.

## SOLID STATE

The particles of a solid are tightly packed and held together by a strong electrostatic force. The particles only vibrate to and fro about an equilibrium or a fixed position. They have a definite shape and volume and very difficult to compress.

## LIQUID STATE

The forces of attraction between molecules of liquids are weak compared to that of solids. Hence they have slight movements. This is why liquids can flow. They have definite volume but not definite shape.

## GASEOUS STATE

As a result of the distance between the molecules of gases, the cohesive forces between them are very negligible and so they move randomly. Gases have no definite shape and volume. They assume the shape of the containing vessel.

EVALUATION

1. What is matter?
2. List and explain the three states of matter.

## COMPARISON BETWEEN SOLID, LIQUID AND GAS

SOLID                              LIQUID                                GAS

1. Fixed mass Fixed mass                               Fixed mass
2. Very dense Less dense                                Least dense
3. Definite shape Shapeless                                 Shapeless
4. Definite volume Definite volume                        No volume
5. Incompressible Incompressible Compressible
6. Particles vibrate Particles vibrate,                       Particles move

a fixed position about a restricted space            at a fixed speed.

EVALUATION

1. Define matter
2. Compare the three states of matter in terms of (a) density (b) compressibility

## TYPES OF CHANGES

Whenever a given substance is heated, its state changes. There are two types of changes: physical and chemical.

### PHYSICAL CHANGE

A physical change is a change which is easily reversible and in which no new substances are formed. Examples are:

1. Dissolution of common salt
2. Changes in states of matter such as melting of solids, freezing of liquids, evaporation of liquids, liquefaction of gases to solids, sublimation of solids.
3. Magnetization and demagnetization of iron nails.
4. Separation of mixture by evaporation, distillation, fractional distillation etc.

EVALUATION

1. What is a physical change?
2. Give two examples of a physical change.

### CHEMICAL CHANGE

A chemical change is a change which is not easily reversible and in which new substances are formed.

Examples of chemical change

1. Rusting of iron/metals.
2. Dissolution of metals and limestone in acids.
3. Fermentation and decay of substances.
4. Changes in electrochemical cells.
5. The addition of water to quick lime.
6. Burning of materials.

## COMPARISON BETWEEN PHYSICAL AND CHEMICAL CHANGES

Physical Change                                Chemical Change

1. Easy to reverse             Difficult to reverse
2. No new substances are New substances are always

formed                                                 formed

1. Very little energy changes There are often large heat

take place                                             change.

1. No change in mass                              The new substances formed have

different masses but the total mass is unchanged.

## GENERAL EVALUATION/REVISION

1. What is a chemical change?
2. Give two examples of a chemical change.
3. State three differences between physical and chemical changes.
4. State the function of the following laboratory apparatuses: a) Fume cupboard b) Burette (c) Bunsen burner

## WEEKEND ASSIGNMENT

1. Which of the following changes is a chemical change? (a) melting of ice (b) liquefaction of air (c) slaking of lime (d) evaporation of a liquid
2. Which of the following substances will occupy a wider space? (a)carbon (iv) oxide (b) liquid milk (c) pieces of chalk (d) water
3. When a solid changes to gas directly, this process is called (a) freezing (b) sublimation

(c) vaporization (d) evaporation

1. Which of the following changes produces a new substance ?(a) reaction of water with sodium chloride (b) addition of acid to base (c) turning of margarine to oil (d) evaporation of water
2. Which one of the following has a fixed shape and volume?

(a) a cube of sugar (b) liquid wax (c) smoke  (d) kerosene

## THEORY

1. Give two differences between physical and chemical changes.
2. Give three processes, which involve a physical change