Estimate the diffusivity of methanol in air at atmospheric pressure and 25ºC.

Question

Estimate the diffusivity of methanol in air at atmospheric pressure and [latex]25^{\circ} C[/latex].

Accepted Answer

Diffusion volumes from Table 8.5; methanol:

Table 8.5. Special atomic diffusion volumes (Fuller et al., 1966)
Atomic and structural diffusion volume increments
C	16.5	Cl	[latex]19.5^{*}[/latex]
H	1.98	S	[latex]17.0^{*}[/latex]
O	5.48	Aromatic or hetrocyclic rings	[latex]-20.0[/latex]
N	[latex]5.69 *[/latex]

Element	No. of
C	[latex]16.50 imes 1=16.50[/latex]
H	[latex]1.98 imes 4=7.92[/latex]
O	[latex]5.48 imes 1=5.48[/latex]
	[latex]\sum_{a} v_{i} \quad \overline{29.90}[/latex]

Diffusion volume for air = 20.1.

1 standard atmosphere = 1.013 bar.

molecular mass [latex]CH _{3} OH[/latex] = 32, air = 29.

[latex]D_{v}=\frac{1.013 imes 10^{-7} imes 298^{1.75}(1 / 32+1 / 29)^{1 / 2}}{1.013\left[(29.90)^{1 / 3}+(20.1)^{1 / 3} ight]^{2}}[/latex] [latex]=16.2 imes 10^{-6} m ^{2} / s[/latex] (8.21)

[latex] ext { Experimental value, } 15.9 imes 10^{-6} m ^{2} / s[/latex]

Element	No. of
C	$16.50 \times 1=16.50$
H	$1.98 \times 4=7.92$
O	$5.48 \times 1=5.48$
	$\sum_{a} v_{i} \quad \overline{29.90}$

Question 8.11: Estimate the diffusivity of methanol in air at atmospheric p...

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