We select to begin our study of matter with the gases state because:
- It is the simplest to study
- It can be readily converted into the condensed states-liquid and solid; hence many of our conclusions concerning gases apply directly to these states.
The assumptions of kinetic theory account for most of the properties associated with gases and we can obtain a better understanding of gas Behaviour.
The Distribution or spreading of gas molecules throughout the vessel is known as diffusion. Unlike liquids or solids, the gases diffuse very rapidly. A Drop of perfume for instance, slowly evaporates out the fragrant gas announce the presence of wearer. It is due to the diffusion of perfume through the air.
In terms of kinetic theory, diffusion is explained as follows. The molecule of gas is widely separated and there are large empty spaces due to which they are free to move. Due to this free movement the molecules of gases intermingle and spread out easily throughout the vessel. The opposite of diffusions is effusion in which gas passes through the pores or tiny holes in the vessel, for example, the air effuses from the tire as a result of which the tire loses pressure gradually.
In contrast to liquids or solids, all gases are easily compressed or squeezed. In terms of ‘kinetic theory’. Gases are easily compressed due to large empty spaces. By applying pressure, the molecules come loser. Air, for instance, is squeezed into automobile tires. When the tire is punctured, the air rushes out. It is the reverse of compressibility – the expansibility, tus volumes of gases are highly affected by the changes in pressure.
All the gases exert pressure. It may appear surprising but it is a fact that we are being pressed upon by an enormously heavy blanket of atmosphere. The mass of atmosphere on our body at seal level and O Celsius is 14.7 psi (pounds per square inch, 1b/in2) or there is about 20 tons total pressure on our bodies.
When a gas is confined in a closed container, it exerts pressure on he walls of the container which is due to the collisions of gas molecules with the walls The tires of automobiles are filled with air until the gauge shows the pressure of about 28 psi. This means that the pressure inside the tire is 28 psi greater than the outside pressure, since the external atmospheric pressure is 14.7 psi, hence the total pressure on the fire is 28 + 14.7 = psi.