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 are very difficult to compress.
Liquid State
The forces of attraction between molecules of liquids are weak compared to those 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
- What is matter?
- List and explain the three states of matter.
Comparison Between Solid, Liquid and Gas
SOLID LIQUID GAS
- Fixed mass Fixed mass Fixed mass
- Very dense Less dense Least dense
- Definite shape Shapeless Shapeless
- Definite volume Definite volume No volume
- Incompressible Incompressible Compressible
- Particles vibrate Particles vibrate, Particles move
and move about rotate and move about constantly
a fixed position about a restricted space at a fixed speed.
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:
- Dissolution of common salt
- Changes in states of matter such as melting of solids, freezing of liquids, evaporation of liquids, liquefaction of gases to solids, and sublimation of solids.
- Magnetisation and demagnetisation of iron nails.
- Separation of mixture by evaporation, distillation, fractional distillation, etc.
Chemical Change
A chemical change is a change which is not easily reversible and in which new substances are formed.
Examples of chemical change
- Rusting of iron/metals.
- Dissolution of metals and limestone in acids.
- Fermentation and decay of substances.
- Changes in electrochemical cells.
- The addition of water to quick lime.
- Burning of materials.
Comparison Between Physical and Chemical Changes
Physical Change Chemical Change
- Easy to reverse Difficult to reverse
- No new substances are New substances are always
formed formed
- Very little energy changes There are often large heat
take place change.
- No change in mass The new substances formed have
different masses but the total mass is unchanged.
EVALUATION
- What is a chemical change?
- Give two examples of a chemical change.
- State three differences between physical and chemical changes.
- State the function of the following laboratory apparatuses: a) Fume cupboard b) Burette (c) Bunsen burner
WEEKEND ASSIGNMENT
- 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
- Which of the following substances will occupy a wider space? (a)carbon (iv) oxide (b) liquid milk (c) pieces of chalk (d) water
- When a solid changes to gas directly, this process is called (a) freezing (b) sublimation
(c) vaporization (d) evaporation
- 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
- Which one of the following has a fixed shape and volume?
(a) a cube of sugar (b) liquid wax (c) smoke (d) kerosene
THEORY
- Give two differences between physical and chemical changes.
- Give three processes, which involve a physical change