Concept of Ideal and Real Gases

CONCEPT OF IDEAL AND REAL GASES

1. Ideal gas:

An ideal gas is an imaginary substance that obeys the relation pV = RT. So, the state equation is also known as ideal gas equation. At low pressure and high temperature, the density of a gas decreases. At that time, the gas behaves as an ideal gas. A factor is introduced to account the deviation of ideal gas behaviour known as compressibility factor. It is a measure of the deviation of ideal gas behaviour.

2. Real gas:

At high pressures, the gases start to deviate from ideal gas behaviour. So, the deviation should be accounted. For accounting this deviation, a factor called compressibility is introduced. The state equation for real gases is given by

pV = ZRT   …..(1.26)

where

Z = Compressibility factor

⸫ Compressibility factor,

Z = pV / RT   …..(1.27)

Compressibility factor can also be expressed by

Z = vActual / vIdeal         ... (1.28)

where

vActual ⇒ Specific volume of real gases

vIdeal ⇒ Specific volume of ideal gases

For ideal gases, Z = 1. But, for real gases, Z is greater than or less than unity. The graph is plotted between pressure, temperature and compressibility to account deviation of ideal gas behaviour.