(a) The mean free path is the average distance a molecule travels before colliding with

Chapter 21, Problem 21-22

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(a) The mean free path is the average distance a molecule travels before colliding with another molecule. The mean free path, , is given by where k is Boltzmanns constant, T is temperature (K), P is pressure (Pa), and is the collision cross section. For a molecule with a diameter d, the collision cross section is d2 . The collision cross section is the area swept out by the molecule within which it will strike any other molecule it encounters. The magnetic sector mass spectrometer is maintained at a pressure of 105 Pa (107 Torr) so that ions do not collide with (and deflect) one another as they travel through the mass analyzer. What is the mean free path of a molecule with a diameter of 1 nm at 300 K in the mass analyzer? (b) The vacuum in an orbitrap mass separator is 108 Pa (1013 bar, 1010 Torr). Find the mean free path in the orbitrap for the same conditions as (a). Chro