Physical Chemistry

The best laboratory vacuum pump can generate a vacuum of about 1 nTorr. At 25 degrees Celcius and assuming air consists of N2 molecules with a collision diameter of 395 pm, calculate (a) the mean velocity of the molecules; (b) the mean free path, and (c) the collision frequency of the gas. [Answers are: 475; 4.3 x 10^4; 0.011]