Write notes on the behaviour of real gases and their deviation from ideal behaviour.

Explanation

Compression factor (Z) is very important to discuss the properties of real gases. It is the ratio of the actual molar volume of a gas to the molar volume of a perfect gas under the same conditions.
Compression factor (Z)
`=("Molar volume of the gas" (V_m))/("Molar volume of perfect gas" (V_mperfect))`
`=(RT)/P`
`thereforeZ=V_m/((RT)/P)=(PV_m)/(RT)`
For a perfect gas , Z=1 .So for other values of Z (other than 1) real gases differ from ideal behaviour.
For real gases, Z varies with pressure At low pressures some gases have `Z lt 1` . From this we can infer that their molar volumes are smaller than that of a perfect gas and the molecules cluster together slightly and attractive interactions are dominant. At high pressures `Z gt 1` for almost all gases. `Z lt 1` means that the molar volume of a gas is greater than that expected for a perfect gas. This is due to dominant repulsive forces which try to derive the molecule apart.
In general, at very low pressures all gases have almost ideal behaviour. At high pressures (Z=1). It is difficult to compress. At intermediate pressures most gases have `Z lt 1` Thus, gases show ideal behaviour when the volume occupied by then is large. Upto what pressure gases follow ideal behaviour ,depends on the nature of the gas and its temperature.
The temperature at which a real gas obeys ideal gas laws over a wide range of pressure is called Boyle temperature of Boyle point and it depends on the nature of the gas. Above Boyle temperature real gases show+ ve deviations from ideality and their Z values are greater than 1. The forces of attractions between the gas molecules are feeble. Below the Boyle temperature , all real gases first show `Z lt 1` with increase a pressure and reaches a minimum. On futher increase of pressure Z constinuously increases. Hence , it may be concluded that at low pressure and high temperate gases show ideal behaviour.