PROPERTIES OF GASES. Introduction. The gas are divided into “real” and “ideal”. The last ones (do not exist in reality) are when intermolecular bombardment forces is equal to 0.
The gas are divided into “real” and “ideal”. The last ones (do not exist in reality) are when intermolecular bombardment forces is equal to 0.
In the gases(air,oxygen,etc.)spacing between molecules is on the order of 10-6 mm, and for the liquids it is on the order of 10 –7 mm.This is because the intermolecular cohesive forces for gases are smaller and their molecules have more kinetic energy and more freedom of motion than liquids. Thus, gases are highly compressible in comparison to liquids.
Table.The values of gas compressibility coefficient z.
Where:dp – the differential change in pressure needed to create a differential change in volume, dV or V
The negative sign is included since an increase in pressure will cause a decrease in volume of a given mass, m = V, will result in an increase in density, Eq.(3) can be expressed as|
E = (5)
The bulk modulus E for gases can be determined by obtaining the derivative dp/d :
E = p; (7)
If the compression is frictionless and no heat is exchanged with the surroundings (isentropic process), then:
Equation (12) is the fundamental equation for fluids at rest. It can be used to determine how pressure changes with elevation. However, to proceed with the integration of Eq. (12) it is necessary to stipulate how the specific weight varies with z.
This is an universal thermodynamic process when all parameters are variable:
n – index of politropy;
c – constant;
After the substitution of Eg.(11) it follows:
After the embedded from Clapeyron p / = R T: