Page 176 - Chemistry ICSE Class IX

7 Study of Gas Laws

Although air was known to the primitive man, the foundations of the
CONTENTS modern concepts regarding the gaseous state were laid in the seventeenth
century. In 1654, Otto von Guericke performed his famous Magdeburg
ͻ WŚLJƐŝĐĂů ĐŚĂƌĂĐƚĞƌŝƐƟĐƐ ŽĨ ŐĂƐĞƐ hemisphere experiment to show that the air exerted pressure.
ͻ DĞĂƐƵƌĂďůĞ ƉĂƌĂŵĞƚĞƌƐ ŽĨ ŐĂƐĞƐ
ͻ ŽLJůĞ͛Ɛ ůĂǁ ;ƉƌĞƐƐƵƌĞͲǀŽůƵŵĞ The actual development of the modern theories for gases began with
ƌĞůĂƟŽŶƐŚŝƉͿ the work of E. Torricelli (Italy) in 1643. Torricelli measured the atmospheric
ͻ ŚĂƌůĞƐ͛ ůĂǁ ;ǀŽůƵŵĞͲ ƚĞŵƉĞƌĂƚƵƌĞ pressure with the help of a barometer.
ƌĞůĂƟŽŶƐŚŝƉͿ It is really a long jump from the natural phenomena to the modern
ͻ ŚĂƌůĞƐ͛ ůĂǁ ĂŶĚ ƚŚĞ ĂďƐŽůƵƚĞ concept of a gaseous atmosphere. In this chapter, we describe the initial
;<ĞůǀŝŶͿ ƚĞŵƉĞƌĂƚƵƌĞ ƐĐĂůĞ stages of the development towards modern concepts about the gaseous
ͻ ZĞůĂƟŽŶƐŚŝƉ ďĞƚǁĞĞŶ <ĞůǀŝŶ ƐĐĂůĞ state.
ĂŶĚ ĞůƐŝƵƐ ƐĐĂůĞ ŽĨ ƚĞŵƉĞƌĂƚƵƌĞ
ͻ /ĚĞĂů ŐĂƐ ĞƋƵĂƟŽŶ
ͻ ^ƚĂŶĚĂƌĚ ƚĞŵƉĞƌĂƚƵƌĞ ĂŶĚ ƉƌĞƐƐƵƌĞ Physical Characteristics of Gases
;^dWͿ ĂŶĚ ŶŽƌŵĂů ƚĞŵƉĞƌĂƚƵƌĞ ĂŶĚ
ƉƌĞƐƐƵƌĞ ;EdWͿ
What are the physical characteristics of gases
All gases show some common characteristics. These are described below:
ƒ Gases maintain neither the volume nor shape, and completely ll the
container in which they are lled.
ƒ Gases expand appreciably on heating.
ƒ Gases are highly compressible, that is, when the pressure is increased,
the volume of a gas decreases considerably.
ƒ Gases exert pressure equally in all the directions.
ƒ All gases, except a few, are colourless. The following gases show
characteristic colours, such as
Fluorine Greenish-yellow
Chlorine Greenish-yellow
Bromine Reddish-brown
Iodine Violet
Nitrogen dioxide Reddish-brown

Measurable Parameters of Gases

What are the measurable parameters of gases

The behaviour of gases can be described in terms of certain parameters.
These are described below.

Mass and amount
Mass of a certain amount of a gas can be obtained by direct weighing.
This can be expressed in any mass unit. The most common unit of mass is
gram (g) or kilogram (kg).