Van Der Waals Gas Equation

[blazinfury]

I am trying to understand exactly what the Van der Waals equation states about the Pressure and Volume of a real gas compared to an ideal gas. Based on the equation, I think that P(ideal)>P(real) because the ideal gas needs to overcome the IMF of attraction since ideal gases have no IMFs; and V(ideal)>V(real) b/c ideal gases occupy no volume and had their volume been smaller, the gas particles would succumb to IMFs.

 

If someone could please correct me if I am wrong and my logic, I would greatly appreciate it. Thank you.

[Xittenn]

Ideal gasses do have a volume but the molecule doesn't. In a real gas if you keep adding molecules the pressure will start to increase as the volume occupied by a single molecule is encroached where an ideal gas does nothing to take this into account. In gasses where there is sufficient volume we will see a contrasting decrease in pressure because of the attractive Van Der Walls forces. I don't think your conclusions about the consequences of each interaction is correct. You need to evaluate the effect of all cases by observing the appropriate graphs and getting a feel for the behaviour through application--something I should probably start doing also.

[Kajal Panda]

• Pressure of the gas is developed due to the wall collision of the gas molecules. But due to inter-molecular attraction, the colliding molecules will experience an inward pull and so pressure exerted by the molecules in real gas will be less than that if there had not been inter molecular attraction as in ideal gas P_i.
• Thus, P_i 〉P
  or, P_i = P + P_a
• Where P_a is the pressure correction term originating from attractive forces. Higher the inter molecular attraction in a gas, greater is the magnitude of P_a.
• Molecules are assumed to be a hard rigid spheres and in a real gas, the available space for free movement of the molecules becomes less then V. let us take the available space for free movement of 1 mole gas molecules,

Vi = (V - b)

• where V is the molar volume of the gas and b is the volume correction factor.
  Vi = molar volume of the ideal gas where the gas molecules are regarded as point masses.