The pressure unit 1 torr is comparable to 0.001 bar. In a sample of N₂ at this pressure and a temperature of 300 K, what is the meal path between collisions in mm (millimeters)? Assume that the cross-section for N₂ molecules is a = 4.50 × 10-19 m².

Determine how many times per second each molecule moving with rms speed would move back and forth across a 6.4 mm -long room on the average, assuming it made very few collisions with other molecules.To find vx use the equation v2=v2x+v2y+v2z and the fact that molecules have no preferred direction.   vrms= 473 m/s

Interstellar space is quite different from the gaseous environments we commonly encounter on Earth. For instance, a typical density of the medium is about 1 atom cm−3 and that atom is typically H; the effective temperature due to stellar background radiation is about 10 kK. Estimate the diffusion coefficient and thermal conductivity of H under these conditions. Compare your answers with the values for gases under typical terrestrial conditions. Comment: Energy is in fact transferred much more effectively by radiation.