Question

What is meant by compressibility factor?

Answer 1

Hint: To answer this question, we should know that it is a useful thermodynamic property for modifying the ideal gas law to account for the real gas behaviour. We should not confuse the compressibility factor with the compressibility.

Step by step answer: We should know about the compressibility factor that it is a correction factor which describes the deviation of a real gas from ideal gas behaviour. We should understand that it is a useful thermodynamic property for modifying the ideal gas law to account for behaviour of real gases. We should also know that it is a measure of how much the thermodynamic properties of a real gas deviate from those expected of an ideal gas.
We should understand this by taking the ratio of the actual volume of a real gas to the volume predicted by the ideal gas at the same temperature and pressure as the actual volume. The compressibility factor is denoted by Z.
$Z=\dfrac{P}{\rho {{R}_{specific}}T}$
In the above formula, p is the pressure, ρ is the density of the gas and ${{R}_{specific}}=\dfrac{R}{M}$ is the specific gas constant, M is the molar mass, and T is the absolute temperature
We should note that for an ideal gas, Z always has a value of 1. For real gases, the value may deviate positively or negatively, depending on the effect of the intermolecular forces of the gas. We should note that the value of Z, generally increases with pressure and decreases with temperature. We should understand that at high pressures molecules are colliding more often. This allows repulsive forces between molecules to have a noticeable effect, making the molar volume of the real gas greater than the molar volume of the corresponding ideal gas it makes Z to exceed one. When pressures are lower, the molecules are free to move. In this case attractive forces dominate, making Z less than one. We should know that the closer the gas is to its critical point or its boiling point, the more Z deviates from the ideal case.
The above paragraph is the explanation of compressibility factor.

Note: We should not confuse compressibility factor with compressibility. Compressibility is the measure of the fractional change in volume per unit increase in pressure. Or we can say that compressibility is a measure of the change in volume resulting from the external pressure applied to the surface of an object.