Chapter 5 Values of diffusion coefficients page 5-1
Chapter 5 Values of diffusion coefficients
1. Diffusion coefficient of CO2 in air
Use Chapman-Enskog Eq. 5.1-1
2. NH4 diffusion in air
3. Water and ethanol
(a) From Table 5.1-2, the radius of ethanol is 4.53/2 = 2.26510-8 cm
At 25°C, the viscosity of water is 0.008937 g/cm-s
-5 2
Use Stokes-Einstein Eqn, D = 1.3810-16*298
6(0.01074)(1.3210-8) = 1.53910 cm /s
4. Diffusion of tobacco mosaic virus
Use Eq. (5.2-2), a = 3000Å = 310-5cm, and b = 150Å = 1.510-6cm
5. Diffusion of lactic acid
The formula of lactic acid is CH3CHOHCOOH, or C3H6O3
(a) In air, because lactic acid is not in Table 5.1-2, we must use eq 5.1-9. From Table 5.1-4,
6. Diffusion of urea
7. Diffusion of Silicates
From Fig. P5.1, –
c1 = 50 mol%, c = 100 mol%, and at z = 5m, c = 80 mol%
1∞1
By substituting these values into Eq. 5.6-3, 0.6 = erf(z/ 4Dt), we found
8. Fast ion diffusion
(b) To convert D into , use eq 6.1-32: D = 2.66210-7 /|z|c
(c) Possibly caused by the unusually nature of vacancies. Details are given in the literature
cited.
9. Molten salt diffusion
The specific conductance is proportional to the flux. Thus we would expect this conductance
to increase linearly with salt concentration, which is consistent with the results at lower salt
concentration. At higher salt concentration, we expect that the rapidly increasing viscosity will
reduce the diffusion and hence conductance. If we want to test this, we can plot conductance
times viscosity (sometimes called the “Walden product”) vs concentration.
0.001
0.01
0.1
1
0.01 0.1 1 10
C (M)
Walden product
We would expect this product to be more nearly constant. In the above figure, the variation
expectation.
10. Diffusion in molten silicate
Chapter 5 Values of diffusion coefficients page 5-4