Laws of Perfect Gases

A perfect gas or an ideal gas may be defined as a state of a substance, whose evaporation from its liquid stat is complete. It may be noted that if its evaporation is partial , the substance is called vapour. A vapour contains some particles of liquid in suspension. The behavior of superheated vapours  is similar to that of a perfect gas.

The physical properties of a perfect gas are controlled by the following three variables

  1. Pressure exerted by the gas
  2. Volume occupied by the gas
  3. Temperature of the gas

The behavior of a perfect gas, undergoing any change in these three variables , is governed by the following laws

  1. Boyle’s Law : Boy’s law was formulated by Rober Boyle in 1662. It states , “The pressure of a given mass of a perfect gas varies inversely as its volume, when the temperature remains constant.”
  2. Charles Law : Charles law was formulated by a Frenchman Jacques A.C. Charles in about 1787. It may be stated in two different forms
    1. “The volume of a given mass of a perfect gas varies directly as its absolute temperature, when the obsolute pressure remains constant.”
    2. “All perfect gases change in volume by 1/273 th of its original volume at 0 degree centigrade for every 1 degree centigrade change in temperature, when the pressure remains constant.
  3. Gay – Lussac law :Gay lussac law states, “The obsolute pressure of a given mass of a perfect gas varies directly as its absolute temperature, when the volume remains constant.”