Question

A vacuum chamber has a base pressure of 10-6 Torr. Assuming that this is dominated by N2 gas where the diameter is 0.44 nm and molecular mass of 28, (a) What is the gas density, the mean free path, the molecule flux at 300 K? (b) What is the partial pressure of O2 that produce a ratio 10-9 of the N2 flux to O2 flux at the same temperature? Considering them have identical diameters

Answer 1

All Units converted to SI Units

(a) The mean free path is given by,

Substituting vaues we get,

The density of gas is given by the ideal gas equation,

Substituting the values we get,

The molecular flux is given by the equation,

Here m is mass of one molecule,

Substituting the values we get,

(b) The molecular flux is directly proportional to the pressure of the gases, and invesely proportional to the square root of mass of the molecule.(Temperature is same and the molecules also have identical diameters). Therefore we can say that,

We know that the pressure by N2 is 10^(-6) Torr and the required ratio is 10:9, Therefore substituting the values we get,

Therefore the partial pressure of O2 should be 6.8 x 10^(-7) Torr.