compressibility factor

Asked by Janaki | 11th Oct, 2010, 10:37: PM

Expert Answer:

Dear Student

Compressibility is a measure of the relative volume change of fluid or solid or gas as a response to a pressure or temperature change.

The compressibility factor is defined as


where, p is the pressure, V is the molar volume of the gas, T is the temperature, and R is the gas constant.


For an ideal gas the compressibility factor is Z = 1 per definition.( We know PV=nRT, is a Ideal gas equation).

To understand the extent of deviation a graph of Z vs p is plotted. The graph will be a straight line parallel to pressure axis for ideal gases. But gases which deviate from ideality, the value of Z will deviate from unity(i.e. 1).  At very low pressures all gases shown to have Z ≈1 and behave as ideal gas.

But at high pressure all the gases have Z > 1. These are more difficult to compress. At intermediate pressures, most gases have Z < 1. Thus, gases show ideal behaviour when the volume occupied is large so that the volume of the molecules can be neglected in comparison to it. 
We hope that clarifies your query.
With Best Regards,

Answered by  | 12th Oct, 2010, 10:32: AM

Queries asked on Sunday & after 7pm from Monday to Saturday will be answered after 12pm the next working day.