mean free path the vacuum distillation section says that li has a greater mean free path than li however the mean free path of an ideal gas does not depend on the speed or mass of the particles where k is the boltzmann constant t is temperature is collision cross section p is pressure since li is lighter it most probably evaporates faster than li since equal kinetic energy results in larger speed for li more li atoms are fast enough to escape but it has nothing to do with mean free path szaszicska from huwiki