Questions tagged [diffusion]
For questions referring to the process by which molecules move as a result of their kinetic energy.
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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 ...
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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/...
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2
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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 ...
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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 ...
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Colour composition of Bromine during diffusion?
Consider the diffusion of Bromine Gas within a tube filled with air.
After a prolonged period of time, is the colour composition uniform?
From my understanding, Bromine is a denser gas. Hence, on ...
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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 ...
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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 ...
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What determines how easily a gas can diffuse into a crystal structure?
I have been told by a metallurgist that the reason a factory oxidizes the iron oxides in ilmenite before reducing them down to pure iron, is that the the products of this have a more spacious crystal ...
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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 ...
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Modelling pH as function of time and position
I already posted this on the Engineering Stack Exchange under Chemical Engineering as I don't know where it's a better fit.
I have a system whose initial state consists of three different sections ...
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Why does the factor of ⅔ come in when we calculate net flux due to diffusion for an ideal gas
As per Atkins' Physical Chemistry (11E) Pg:694. We arrive at a crude estimate for the net flux through an imaginary flux plane. We find it to be $$J_{z}=-\frac{1}{2}v_{mean}\lambda(\frac{d\mathcal{N}}{...
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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 ...
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2
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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 ...
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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.
...
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Why is the Einstein relation not valid for germanium?
In Elecronic Devices and Circuits, by J Millman and CC Halkias, it is written at one place:
.....coefficient of diffusion $D$ and mobility $\mu$ aren't independent. The relationship between them is ...
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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 ...
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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 (...
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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 ...
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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 ...
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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)....
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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 ...
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Diffusion of particles across a plane surface
A relatively viscous material is coated with a thin film consisting of gold nanoparticles that can diffuse into the material. We can assume that all particles have a diameter of $\pu{25 nm}.$ Coating ...
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A physical meaning of the Danckwerts boundary condition in terms of concentration profile (adsorption)
Can someone please explain to me in a simplified way, what exactly does a well-recognized Danckwerts boundary condition do to the concentration profile of adsorption phenomena? I just cannot find a ...
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Molecular diffusivity of a three-component mixture
I usually used a following expression by Fuller & Schettler & Giddings to predict molecular diffusivities of binary mixtures:
\begin{equation}
D_i = \dfrac{1\cdot 10^{-4}\left(0.00143\cdot T^{...
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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?
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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 ...
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2
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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 ...
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What is b in the Gompertz model?
I am wondering how to use the Gompertz model in modelling drug diffusion:
$$x(t) = x_\mathrm{max}\exp(-a\exp(b\log t)).$$
$x_\mathrm{max}$ is to be taken as $100,$ $a$ is the undissolved proportion at ...
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How does stirring demonstrate a diffusion-controlled reaction?
I was reading about diffusion-controlled reactions, and on the Wikipedia page (Diffusion-controlled_reaction) it says the following:
"One classical test for diffusion control is to observe ...
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Relation of temperature to effusion and diffusion [duplicate]
We were studying Graham's Law today and its dependence on Temperature, Pressure, Area, etc.
However, our teacher said that, for diffusion: $$R \propto \sqrt T$$ and for effusion:$$R\propto1/\sqrt T$$ ...
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1
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Do the concepts of Newtonian and non-Newtonian fluids still hold at a nanoscopic level?
Recently I've spent a great deal of time thinking about enzyme diffusion in cytoplasm. One thing that keeps me awake at night is the constant referral to cytoplasm as a non-Newtonian fluid (which it ...
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How do I compute the mean dissociation time from the dissociation constant, assuming instantaneous binding reaction rate?
There is a solution with two chemical species, A and B. Given the equilibrium dissociation constant
$
K_D=\frac{[A][B]}{[AB]}
$
how do I relate the mean dissociation time $t_{off}$ to $K_D$, and ...
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1
answer
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Indirectly Measuring Diffusion of NO2 into Water
I am working on a data science project with the central hypothesis is that air-born pollutants can become water-born through diffusion. The example I am using as a proof of concept is $\ce{NO2}$. The ...
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What unit and dimension for membrane permeability / permeation expression?
Context
When studying the diffusion of gases through thin membrane, one may use the diffusion coefficient $D$ used in Fick's laws as (one dimension form):
\begin{equation}
J = - D \cdot\frac{d\varphi}{...
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Porous materials: Is the expression of a mean free path $\overline{\ell}$ of the gas molecule valid for a binary mixtures?
Suppose that I have a binary gas mixture at low pressure. Can I calculate the mean free path $\overline{\ell}$ of the gas molecule in a pores of solid material by substituting a molecular weight of a ...
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Boundary conditions in a closed system for diffusion (2nd Fick's law) in a porous medium
I would like to calculate the chloride redistribution in concrete (assumption: porous and homogeneous structure, purely diffusion-controlled mass transfer, closed system). For this I have derived a ...
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How do concentrations of different solutes across a cell membrane affect whether water leaves or enters the cell?
I know from class that water travels to where the solute concentration is higher. I have no problem visualizing it if it's just "salt." What if there are multiple types of solutes? For ...
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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 ...
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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 ...
user66707
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1
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If Graham's law doesn't apply to the ammonia and hydrogen chloride diffusion in a glass tube demonstration, is there a law that does?
A comment below What exactly are "white fumes" and why does holding a bottle of ammonia (conc) next to a bottle of HCl (conc) make them? links to The
Royal Society Of Chemistry video ...
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Why does ink form tendrils on wet paper [closed]
When a drop of ink or watercolour paint is placed on wet paper, rather than uniformly diffusing in all directions it forms tendrils which rapidly expand out from the spot.
Why is this and what is the ...
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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 ...
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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}}}...
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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:
$\frac{...
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Redefine a Mixing Modulus based on new reaction scheme
I am studying the effect of diffusion on liquid chemical reactions. The model is very simple in that it assumes that striations or slabs of fixed thickness of one reactant are next to the other. ...
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Diffusion rate of drugs - Ficks model?
I have a question about diffusion rate of a slow release drug. The drug I've been taking has an extended-release formulation and contains beads encapsulated in a capsule.
The beads are coated with a ...
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How to minimize sample dispersion during spotting for paper electrophoresis?
I am separating highly polar amino acids and their derivatives using paper electrophoresis. This requires pre-wetting a piece of filter paper with electrophoresis buffer (in this case, carbonate-...
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Relationship between molar flux and density of current
I am studying the mass transport for a charged species in a stirred solution. So, I have obtained the Nernst-Planck equation:
\begin{equation}
\mathbf{J} = -D\nabla C - \frac{zFDC}{RT}\nabla \phi + C\...
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Brownian motion of asymmetric particles
The classic Stokes-Einstein relation ($D=k_BT/(6\pi\eta r)$) it is assumed that the particle undergoing Brownian motion is spherical, and experiences ordinary Stokes flow between (or during) ...
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Diffusion coefficient for acid base reaction
I am trying to model an acid-base neutralization reaction. There are two adjacent slabs - one acid and one base. Each slab is the same thickness and I'm only looking at one-dimensional diffusion/...
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