Example 4.2:
A cylinder containing hydrogen at 400 K, 1 atm is placed in an evacuated chamber. If a hole of area 0.03mm² is made in the cylinder. Calculate the number of molecules leaking through the hole per second. Take the average velocity of the molecules as 0.725 of the rms speed.

Solution:

For hydrogen,

Rate of flux of molecules per unit area 

Rate of hydrogen leakage through the hole