Questions tagged [diffusion]
For questions referring to the process by which molecules move as a result of their kinetic energy.
39
questions
15
votes
1answer
202 views
Is there a consensus on whether amber can seal in air bubbles for millions of years?
I read about deriving the oxygen content in the atmosphere in the Cretaceous by analyzing the air trapped in bubbles in amber from that period, but I have also found papers disputing the study's ...
11
votes
2answers
170 views
How is the water escaping?
I have a number of toy balls filled with a liquid-presumably water or something else non-toxic. Over about a year, the balls have gone from firm to indented as shown. The water level in one is visibly ...
8
votes
4answers
6k views
Why is entropy favorable?
I cannot seem to grasp the logic behind it. We say that more entropy (or more disordered system) is favorable over less entropy. But why? Why is randomness preferred over proper arrangement of atoms/...
7
votes
3answers
2k views
When is diffusion steady-state?
Fick’s first law of diffusion can be used when $\mathrm{d}C/\mathrm{d}t=0$. If the concentration gradient is time-variant, then we must use Fick’s second law. However, when is diffusion steady-state ...
5
votes
1answer
35 views
How to make equal density pool dye without diffusion
I have a leak I have been struggling to find in my in-ground pool. I am losing about 1/4" of water per day and I believe the issue is one of the fittings in the bottom of the pool. There are two ...
5
votes
0answers
132 views
How to account for the interface between two different phases in a discretized diffusion model?
I have tried to set up a model for the diffusion of a gas into a liquid. The two media are next to each other and the geometry is spherical because the system should simulate the diffusion out of a ...
4
votes
1answer
123 views
Diffusion across a thin film
Given this concentration profile, I am to (1) determine at which side substance A will diffuse out of the membrane and (2) chose one of the following profiles below which represents the concentration ...
4
votes
0answers
115 views
Reaction-diffusion equation using Lattice-Boltzmann method
I'm struggling to get a working LBM reaction-diffusion implementation. I have a pretty weak mathematics and physics background, and thus I'm having a hard time understanding the notations around the ...
3
votes
1answer
131 views
Is there a known relation between the diffusion of a molecule and the diffusion of the reactants?
I have a plasma consisting of elements A and B (which have a similar mass). These elements can react to form molecules AB.
$$
\ce{A + B -> AB}
$$
Now if my plasma or gas is expanding based on ...
3
votes
1answer
91 views
Cause of imaginary part of Warburg element in EIS
In electrochemical impedance spectroscopy experiments (EIS) the diffusion of electroactive species at flat, macroscopic electrodes is commonly described by the Warburg element with the impedance ...
3
votes
1answer
101 views
What kind of unit is this [A*m^2/mol]?
I found a term on this website that gives a unit of [A*m^2/mol]. The equation is:
$k_d^{eff}=\frac{2RT\kappa^{eff}}{F}(t^+-1)\left(1+\frac{\text{d}\ln(f)}{\text{d}\ln(c)}\right)$
where R is the gas ...
3
votes
0answers
29 views
Are there materials permeable to oxygen and carbon dioxide but not nitrogen?
Are there materials permeable to $\ce{O2}$ and $\ce{CO2}$ but not $\ce{N2}$?
Would this even be possible in theory? Can it be done at even at pressures of 300 atm?
3
votes
0answers
41 views
Limit to volume change in a discretized mathematical model?
I have set up a mathematical model describing the diffusion of ozone out of a gas bubble. The bubble is surrounded by a thin gas film. So actually, the model describes the diffusion of ozone through ...
2
votes
2answers
263 views
Determine direction of mass transfer
For part a) I don't really know what to look at. Diffusion occurs from low to high concentrations so by looking at $t_1$ I would say that the direction of the mass transfer is from phase II (organic ...
2
votes
2answers
93 views
how to display diffusion to a young audience?
I need to display some science topic pertaining to the atomic bombs, or atomic history in some way to children of approximately middle school level. So I've decided that something interesting to cover ...
2
votes
1answer
157 views
Are there any solids that undergo diffusion?
Are there any solids that undergo diffusion?
Introduction:
In school, my teacher is only talking about diffusion happening in liquids and I though that it may be able to happen to solids also.
...
2
votes
2answers
361 views
Is pressure equalization “diffusion”?
There is another question on the site which is:
Two containers, A and B, connected by a closed valve were evacuated and the Chlorine gas (Cl2) with a pressure of 200kPa was put into A and Oxygen (...
2
votes
3answers
331 views
Where to buy/How to build a Devanathan-Stachurski cell?
I'm preparing to do some hydrogen permeation tests to calculate the diffusivity of some iron samples. I would like to do this using the Devanathan-Stachurski cell, which consists of two cells, one ...
2
votes
1answer
91 views
Why does water diffuse from a lower solute concentration to a higher one?
I'm studying biology and this came up in the context of passive transport. I understand why, in general a gas moves down a concentration gradient (the random movement of gas particles and probability)....
1
vote
1answer
545 views
How can I get self-diffusion coefficient from MSD (mean sqaure displacement)
I run some molecular dynamic simulations for polymer system (liquid), and I have data of MSD vs t(time). MSD-t relation looks linear proportional. Now, which one is the proper way to calculate the ...
1
vote
1answer
214 views
Dependency of rate of diffusion on mean free path and velocity of molecules? [duplicate]
What is the dependency of rate of diffusion ( Graham's law) on mean free path, molecular size , average velocity, collision frequency and pressure? I have searched everywhere on internet but just ...
1
vote
1answer
36 views
Effective diffusion coefficient of a species in a heterogeneous mixture
I want to calculate the effective diffusion coefficient of hydrogen radical in a mixed-phase consisting of metal oxide, metal hydride and metal. I consider the interfaces to be diffuse.
How can I ...
1
vote
1answer
102 views
Derivation of formula used in calculating molecular mass from a mixture
In a solution to a problem, to calculate Molecular mass of unknown gas from a mixture containing $\ce{O2}$ in $80~\%$, the author used the formula :
$\frac{1}{\sqrt{M_\text{mix}}}=\frac{X_{\ce{O2}}}...
1
vote
1answer
3k views
Graham's law of diffusion
The rates of diffusion of two gases $\ce{A}$ and $\ce{B}$ are in the ratio $1:4$. If the ratio of their masses present in the mixture is $2:3$, the ratio of their mole fraction is?
My tries:
$\frac{...
1
vote
0answers
18 views
Tungsten-Rhenium alloy connections to Copper. Methods?
I want to use some fine WRe wire (50 micron diameter, 80/20) in a particular environment where it has to conduct a few millamps of current while supporting 100g of mass. The problem being the contact ...
1
vote
0answers
39 views
What makes the odor of flatulence fade away? [closed]
If an individual expelled their intestinal gas in an enclosed space, that smell would seemingly fade away. Why is this so? I would think of 3 possible explanations:
The gases dilute in the air. If ...
1
vote
0answers
37 views
Fick's second law atomic diffusion question [closed]
I have a question about diffusion and i'm not sure how to tackle it.
A new processing method is being tried for a lithium battery cathode material -LiCoO2. the process leaves the ceramic oxygen ...
1
vote
0answers
61 views
Molar flux through membrane
Consider a liquid of pure $\ce{A}$ covered by a composite membrane through which
the vapor of $\ce{A}$ is diffusing. The membrane consists of two layers of thickness $l_1$ and $l_2$. The diffusion ...
1
vote
0answers
29 views
Diffusion equation I can't seem to find anywhere
So I was looking through some old lecture notes from a few years back when I stumbled upon a useful and simple equation that should, according to my former professor describe the diffusion in solid ...
1
vote
0answers
66 views
What coefficients can I use in a Reaction-Diffusion Equation?
I am qualitatively analyzing an abstract chemical reaction
$A + B \rightarrow 2A$
where $A$ and $B$ are some liquid substances that undergo Reaction-Diffusion with a second order reaction (actually ...
1
vote
0answers
215 views
How to write mass balance equation for the scenario when molecules are getting generated inside an sphere?
I am working on the physical understanding of diffusion through a nano machine(a shell with hollow interior in which molecules are produced) and have taken few assumptions:
There is rate $r_T$ with ...
0
votes
1answer
31 views
Is the solution isotonic, hypertonic, or hypotonic?
The problem is shown below. I don't understand how can the tonicity of a solution be determined if the solution has multiple solutes dissolved in it.
Do I take the total sum of the mass of solutes ...
0
votes
2answers
636 views
Diffusion rate of gases
What is the effect of temperature on diffusion rate of gases? Do the diffusion rates of gases decrease with an increase in temperature? Why?
I just read it somewhere that the diffusion rate of gases ...
0
votes
2answers
96 views
Is it possible to solve the equation for the diffusion of gas through a sphere analytically by applying e.g. “combination of variables”?
In the case of diffusion through a thin film it is possible to combine the variables in the following way:
$\sigma = \frac{x}{\sqrt{4Dt}}$
where
$x$=length
$D$=diffusion coefficient
$t$=time
$\...
0
votes
1answer
100 views
What is the reason for phase separation? [closed]
I have seen phase separation as a phenomenon taking place. However I do not understand why this phenomenon occurs as a counter example to the natural laws of diffusion along the concentration gradient....
0
votes
1answer
326 views
Why do two solutes permitted to diffuse simultaneously across a semi-permeable membrane both end up at equal concentrations on both sides?
Let's say we have solute a, which is highly concentrated (let's say 99%?) on side 1 of a semipermeable membrane.
We also have solute b, which is has a much lower concentration (let's say 0.01%) on ...
0
votes
1answer
220 views
Diffusion experiment with dialysis membrane bag
Recently I have performed a diffusion experiment with a dialysis membrane containing methylene blue. A schematic picture of the experiment:
I want to calculate the flux (amount diffused/area*time) ...
-1
votes
1answer
260 views
Effect on rate of diffusion in addition of an inert gas
What will be the effect on the rate of diffusion on addition of an inert gas to the gaseous mixture?
I think the rate of diffusion should increase as the addition of extra gas will increase the ...
-2
votes
1answer
361 views
Why do universal indicators in titration have to be swirled?
Why do universal indicators in titration have to be swirled?
Here's a specific example: I am using methyl orange along with hydrochloric acid to test the alkalinity of a set of household cleaners (...
