General Characteristics of Gases. Gases possess the following general characteristics :
(i) Shape and volume: Gases have neither definite shapennor definite volume. They take up the shape and volume of the container. Only 11 elements existing as gases
(ii) Density: They have lower density than liquids and solids. under normal conditions
(iii) Compressibility: They are highly compressible.
(iv) Diffusability: Gases intermix completely in all proportions without any mechanical aid.
(v) Pressure: They exert pressure equally in all directions.
The above properties are due to the fact that intermolecular forces of attraction among the molecules of a gas are negligible.
In addition to the various properties of gases listed above, gases obey certain laws, called 'Gas la.' which have been discovered as a result of experimental studies. These laws give quantitative relationships between mass, volume, pressure and temperature of the gas. The aim of the present section is, therefore, first to discuss the measurement of these properties of a gas and then to discuss some of the gas laws obeyed by the gases.