Click to Chat
0120-4616500
CART 0
Use Coupon: CART20 and get 20% off on all online Study Material
Welcome User
OR
LOGIN
Complete Your Registration (Step 2 of 2 )
if there exists no ideal gas, then how can we apply the gas equations for the real gases???? How do we know the temp limit for the formulae to be applicable????
6 years ago
Share
Dear priyanka,
All gases are known to exist as real gases and show ideal behaviour only to some extent under certain conditions. When PV = nRT for ideal gases, then the ratio
For real gases Z may be less or more than one. If Z<1 then it is called negative deviation which means that the gas more compressible. if z>1 then the gas is less compressible and it is called positive deviation. It is observed that the deviations are low at low pressures. At high pressures the deviations depends on the nature of the gas.
A plot of versus P for some common gases are shown in the figure.
Fig: 2.7 - Plot of compressibility factor as a function of P
For H_{2} and He, 'Z' is greater than one while for N_{2}, CH_{4} and CO_{2} 'Z' is lesser than one. This means that these gases are more compressible at low pressures and less compressible at high pressures than expected from ideal behaviour.
The effect of temperature on the behaviour of real gases is studied by plotting the value of 'PV' against temperature. It is observed that the deviations from ideal behaviour is less with the increase in temperature.
Thus, real gases show ideal behaviour at low pressures and high temperatures.
In order to know the causes for deviations from ideality, Van der Waal pointed out the faulty assumption that were made in formulating the kinetic molecular model of gases.
Hence, Van der Waal who incorporated the idea of finite molecular volume and intermolecular forces modified the Ideal Gas Equation as follows:
V_{c}_{o}_{r}_{r}_{e}_{c}_{t}_{e}_{d} = (V-nb) for 'n' moles.
Correction due to intermolecular forces is considered in terms of the pressure. A molecule at the wall of the container experiences an inward pull due to attractive intermolecular force of the neighbours. The molecules strike the wall with a lesser force and so the observed pressure is less than the ideal pressure. The pressure correction term
Substituting these values for pressure and volume, the ideal gas equation can now be written as:
This equation is Van der Waal's equation of state. Here, the constant 'a' measures the forces of attraction between the molecules of the gas and 'b' relates to the incompressible volume of the molecules, measuring the size of the gas molecules.
We are all IITians and here to help you in your IIT JEE preparation. All the best.
If you like this answer please approve it....
win exciting gifts by answering the questions on Discussion Forum
Sagar Singh
B.Tech IIT Delhi
Related Question
Post Question
Dear , Preparing for entrance exams? Register yourself for the free demo class from askiitians.
Email :
Name :
Mobile :
Grade :
Subject :
Demo Date :
points won -