Question

a) The stratosphere extends to 50 km above the Earth’s surface, where P = 0.085 kPa and T = 18.3° C.

What is the mean free path and collision frequency of N2 at this altitude?

b) Describe the variation in mean free path with temperature for a gas at constant volume?

Answer 1

Assume:

σ = 0.43 nm²

then...

P = 0.085 kPa

WL = RT/(sqr(2) * Na *σ * P)

WL = (8.314)(18.3+273) / (sqrt(2) * (6.022*10^23) * (0.43 *10^-18) * (0.085*10^3))

WL= 0.00007780497 m = 7.78*10^-5 m

the mean free path is then 0.00007780497 m = 7.78*10^-5 m

b)

Temperature is directly proportional to the mean free path, as you can see from the equation:

WL = RT/(sqr(2) * Na *σ * P)

therefore, an increase in T, is marked in the free mean path

the higher T, the higher mean path