[diablo]

Hi folks,

i got problems with solving exercise:

Calculate the collission frequency (z) of 1 single He-atom with other atoms (time = 1sec, T= 303K, p  0,1bar, sigma = 0,21nm²) Answer = 9,0x 10¹⁰,

Formular --> z = sigma*c_rel*N .
Formula for N = p/kT
Formula for c_rel = c*2^1/2... and 
Formula for c = ((8*R*T)/pi*M))^1/2. M = 0,004kg (He)

sigma = 0,21nm²
p= 0,1*10⁵ (Pa)
T= 303K
k= 1,31*10^-23 J/K
R= 8,31

when i put those values in the formulas, i get ~ 9,0* 10^{^19} and not9,0* 10¹⁰

whats wrong ?

[Yggdrasil]

Check your units (recall 1 bar = 10⁵ Pa = 10⁵ kg m^-1 s^-2 and 1 J = 1 kg m² s^-2).

[diablo]

Thx for your answer,

i checked my units and i finally get ms^-1

z= simga (nm²) * c_rel*N

for c_rel i get the units J/(mol*kg)
for N i get the units (kg*mol)/(m*s*J)

Reducing c and N would result in 1/(m*s) --> multiplied with sigma the final unit would be m/s ?

[Yggdrasil]

The correct units for N are mol m^-3.   Try rechecking the calculation.

[diablo]

now i get m/s², thats the unit of acceleration 

are the formulars which i've written down correct?