Gaseous state
Various kinds of substances that constitute matter can be roughly divided into three categories namely- gases, liquids and solids. The existence of matter in either of these three forms is a result of the competition between two opposing intermolecular forces
(1) The forces of attraction, which hold the molecules together.
(2) The thermal energy of these molecules which tend to increase the intermolecular distances.
If the thermal energy of the molecules is much greater than the forces of attraction, the state of matter that result is called the gaseous state. On the other hand, if the forces of attraction are greater than the thermal energy, we have the matter in the liquid state. When these forces of attraction are much more greater than the thermal energy compared to the liquid state, we have matter in its solid state condition. However, on the application of heat, the thermal energy of the molecules can be increased and as a result the intermolecular forces of attraction would relatively decrease simultaneously.
Molecules in the gaseous state possess high energy and have almost no force of attraction. They are far apart and show a great uniformity in behaviour, irrespective of their chemical nature, colour or odour. They are highly compressible and can also be expanded without limit. They also produce pressure on the walls of any container uniformly in all directions. They diffuse rapidly through one other to form a homogeneous mixture, and their separation is also not very easy.
Gas laws
Boyle’s law
At constant temperature, the volume of a sample of gas of definite mass varies inversely with its pressure.
i.e when temperature is kept constant for a given mass of gas
where V = volume and p = pressure
Introducing a constant k, we have
pV = k = constant …(1)
The value of the proportionality constant k depends upon the following factors:
(1) Nature of a gas
(2) Temperature of the gas, and
(3) The mass of the gas
Hence, at constant temperature, for a given mass of a gas, Boyle’s Law states
p1V1 = p2V2 = k = constant …(2)
Eq. (1) can be represented graphically as shown in figure given below.
The general term isotherm (i.e. at const. Temp.) is used to describe the above curves.
