Question

The pressure of real gas is less than the pressure of an ideal gas because of:

• A. Increase in collisions
• B. Increase in intermolecular forces
• C. Infinite size of molecules
• D. Statement is incorrect

Answer 1

Answer: (B)

Van der Walls noted that the total force of attraction on any molecule about to hit a wall is proportional to the concentration of neighbouring molecules, n/V. However, the number of molecules about to hit the wall per unit wall area is also proportional to the concentration n/V. Therefore, the per unit wall area, or pressure,is reduced from that assumed in the ideal gas wall by a factor proportional to $n^2/V^2.$ Letting a be the proportionality constant, we can write

$P\left(actual\right)=P\left(ideal\right)-n^{2}a/V^2$

$P\left(ideal\right)=P\left(actual\right)-n^{2}a/V^2$