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CHAPTER 5 : STATES OF MATTER

5.1 The Physical Status of Matter

There are mainly three different kinds of the physical states of matter, namely:
- Solid
- Liquid
- Gas

Plasma a fourth class of matter has also been identified. These states of matter are also termed as phases.

1) Solid : Solids are characterized by their definite shape and also their considerable mechanical strength and rigidity. Solids tend to resist the deformation of their shape due to strong intra molecular forces and absence of the translatory motion of the structural units (atoms, ions etc). A solid is relatively non compressible, i.e. temperature and pressure have only a slight effect on its volume.

Solids are broadly classified as crystalline or amorphous.

Crystalline solids : Here the atoms are arranged in a definite pattern which is constantly repeated.

Amorphous solids : These have no definite geometrical form.

2) Liquid : A liquid has no definite shape and it takes the shape of the vessel containing it. Like solids, the volume of a liquid is slightly altered by variations in temperature and pressure. Liquids have three typical physical properties, namely:

i) Vapor pressure : A Liquid when kept in a closed container vaporizes into the free space above it. The process of vaporization will continue till the equilibrium is reached between liquid and vapor. The pressure at which the liquid and vapor can co-exist is called the vapor pressure of the liquid at a given temperature.

ii) Surface tension : The surface of a liquid is always in a state of tension because a molecule at the surface is attracted towards the bulk by a force much greater than that drawing it toward the vapor where the attracting molecules are more widely spread. Due to this, a certain force is required to penetrate along any line in the surface. This force is called surface tension.

iii) Viscosity : It determines the flow of the liquid. It is the internal friction between layers of the liquid. Higher the rate of friction, greater the viscosity of the liquid and its flow will be retarded. Conversely, a lower rate of friction lessens the viscosity and makes the liquid more fluid.


3) Gases : A gas has no bounding surface at all and will occupy completely any vessel in which it is filled. It has no definite volume or shape and can be easily expanded or compressed.

Laws governing behavior of gases will be dealt with in detail in the next chapter.

Water is the ideal example to show the different states of matter.

Water when cooled to 00C becomes solid. When the temperature of solid water is raised it becomes liquid. If the liquid is heated to 1000C it gets converted to steam or vapor (The Gas phase).

Almost all chemical substances can exist in more than one physical state (phase) depending on external pressure and temperature.

The following table illustrates different states of matter and their physical properties.

Table 9

 

Property

States of matter

 

 

Solid

Liquid

Gas(Vapor)

i)

Shape

definite

indefinite

indefinite

ii)

Volume

definite

definite

indefinite

iii)

Molecular
Bonding

very strong

strong

Weak

iv)

Examples

NaCl

ZnSO4

H2O

Petrol

H2 , CO2

LPG

 

 

The Molecular mode of Solids, Liquids, Gases

Plasma : This is the fourth state of matter. It is a type of gas containing positively and negatively charged particles in approximately equal numbers and present in the sun and most stars.

Index

5.1 Solids, Liquids and Gases
5.2 Phases
5.3 Nature of Heat

Chapter 6





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