Reduced Properties and Principle of Corresponding States

REDUCED PROPERTIES AND PRINCIPLE OF CORRESPONDING STATES

Each gas behaves in its own way for the given pressure and temperature. So, the correction factor can be set for each property of gas such as pressure, p and temperature, T to know the thermodynamic behaviour for any gas by normalizing the properties. Therefore, the pressure, p and temperature, T are normalised with respect to their critical values such as pc and Tc. Now, the correction factor can be calculated as follows.

So, the correction factors of pressure and temperature are called reduced properties. The normalised pressure, pr is called reduced pressure and it is given by the equation (5.35). Similarly, the normalised temperature Tr is called reduced temperature and it is given by the equation (5.36). The compressibility factor will approximately be the same for the same pr and Tr values. It means, substances at corresponding states behave alike. It is called principle of corresponding states.