1. 21.4 Transport properties of a perfect gas
Experimental observations on transport properties shows that the flux of a property is proportional to the first derivative of other related properties.
The flux of matter is proportional to the first derivative of the concentration (Fick’s first law of diffusion): J(matter) 
The rate of thermal conduction is proportional to the temperature gradient: J(energy) 
J(matter) = D is called the diffusion coefficient (m2s-1);
J(energy) = - k dT/dz k is called the coefficient of thermal conductivity (J K-1 m-1 s-1)

3. J(x-component of momentum) = , η is the coefficient of viscosity.

4. Table 21.3

5. Diffusion

6. As represented by the above Figure, on average the molecules passing through the area A at z = 0 have traveled about one free path.
The average number of molecules travels through the imaginary window A from Left to Right during an interval Δt is
ZwA Δt (L→R)
Because Zw = So A Δt (L→R)
The average number of molecules travels through the imaginary window A from Right to Left during an interval Δt is
A Δt (R →L)
The net number of molecules passing through the window A along the z direction is:
A Δt A Δt
By definition the flux of molecules along z direction can be calculate as
J(z) = ( A Δt A Δt )/(A Δt )
J(z) =
The number density N(-λ) and N(λ) can be represented by number density N(0) at z =0
N(-λ) = N(0) - λ N(λ) = N(0) + λ
Therefore: J(z) =
then we get D = (different from what we expected)

7. A factor of 2/3 needs to be introduced.
So we get
D =

8. Thermal conduction
k =
where CV,m is the molar heat capacity at constant volume.
Because λ is inversely proportional to the molar concentration of the gas, the thermal conductivity is independent of the concentration of gas, and hence independent of the gas pressure.
One exception: at very low pressure, where the mean free path is larger than the size of the container.

9. J(x-component of momentum) = , η is the coefficient of viscosity.

10. Viscosity The viscosity is independent of the pressure.
Proportional to T1/2

11. Measuring the viscosity
Poiseuille’s formula:

12. Calculations with Poiseuille’s formula
Example: In a poiseuille flow experiment to measure the viscosity of air at 298K, the sample was allowed to flow through a tube of length 100cm and internal diameter 1.00mm. The high-pressure end was at 765 Torr and the low-pressure end was at 760Torr. The volume was measured at the latter pressure. In 100s, 90.2cm3 of air passed through the tube.
Solution: Reorganize Poseuille’s equation: