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Questions tagged [diffusion]

For questions referring to the process by which molecules move as a result of their kinetic energy.

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15 votes
1 answer
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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 ...
Oosaka's user avatar
  • 253
12 votes
4 answers
13k 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/...
completely newbie's user avatar
12 votes
2 answers
1k 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 ...
MattD's user avatar
  • 123
8 votes
3 answers
3k 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 ...
lightweaver's user avatar
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5 votes
2 answers
502 views

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 ...
Beamon's user avatar
  • 69
5 votes
1 answer
182 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 ...
SouthernYankee65's user avatar
5 votes
0 answers
147 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 ...
Sigils's user avatar
  • 191
4 votes
2 answers
500 views

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 ...
user110391's user avatar
4 votes
1 answer
347 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. ...
ca1c's user avatar
  • 143
4 votes
1 answer
484 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 ...
katara 's user avatar
  • 1,095
4 votes
1 answer
114 views

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 ...
Iridium's user avatar
  • 67
4 votes
0 answers
72 views

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}}{...
Uranium238's user avatar
4 votes
0 answers
148 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 ...
nicoco's user avatar
  • 141
3 votes
2 answers
526 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 ...
lotte07's user avatar
  • 187
3 votes
1 answer
82 views

Convection or Advection term in the Absolute flux of a chemical species

I am confused as I have been reading on mass transport on multiple sources and they seem to use "advection" and "convection" interchangeably in the equation for the absolute flux ...
RMS's user avatar
  • 233
3 votes
1 answer
128 views

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 ...
Awe Kumar Jha's user avatar
3 votes
1 answer
64 views

Graham's Law for mixtures?

If we have a mixture of (ideal) gases, what is the rate of diffusion of the total mixture? Also, what are the rates of diffusion of the individual components? My teacher said it was inversely ...
Marc Carlsan's user avatar
3 votes
3 answers
790 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 ...
tcritch's user avatar
  • 129
3 votes
2 answers
682 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 (...
MaxW's user avatar
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3 votes
1 answer
149 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 ...
PoorYorick's user avatar
3 votes
1 answer
291 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 ...
Jens's user avatar
  • 131
3 votes
1 answer
163 views

Smell of orange peel travels super fast

Many years ago, my college chemistry teacher squeezed an orange peel in the front of the auditorium asking us to raise our hands when we smelled it. Hands rippled through the auditorium (at least 40 ...
Greg's user avatar
  • 139
3 votes
1 answer
3k 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)....
gardenhead's user avatar
3 votes
1 answer
158 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 ...
Physther's user avatar
  • 944
3 votes
0 answers
58 views

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 ...
katara 's user avatar
  • 1,095
3 votes
0 answers
645 views

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 ...
Josh E.'s user avatar
  • 133
3 votes
0 answers
49 views

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^{...
Josh E.'s user avatar
  • 133
3 votes
0 answers
53 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?
Algebraist's user avatar
3 votes
0 answers
46 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 ...
Sigils's user avatar
  • 191
2 votes
2 answers
128 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 ...
tox123's user avatar
  • 957
2 votes
2 answers
271 views

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 ...
Petra's user avatar
  • 31
2 votes
2 answers
272 views

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 ...
Jack's user avatar
  • 51
2 votes
1 answer
54 views

Would microelectrodes reach a steady state current if convection is negligible and only pure diffusion occurs?

Assuming a two dimensional Cottrell type problem with a micro-electrode and a high enough applied potential so that concentration of the consumed redox species would be zero near the surface. ...
Youssef Khar's user avatar
2 votes
1 answer
536 views

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:$$R\propto1/\sqrt T$$ ...
stonecraft bros's user avatar
2 votes
1 answer
82 views

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 ...
Bdrs's user avatar
  • 733
2 votes
1 answer
141 views

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 ...
Ferdinando Randisi's user avatar
2 votes
1 answer
99 views

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 ...
E Tam's user avatar
  • 149
2 votes
0 answers
360 views

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}{...
mranvick's user avatar
  • 536
2 votes
0 answers
22 views

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 ...
Josh E.'s user avatar
  • 133
2 votes
0 answers
96 views

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 ...
user88858's user avatar
1 vote
1 answer
115 views

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 ...
geneticscodingnoob's user avatar
1 vote
1 answer
7k 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 ...
exsonic01's user avatar
  • 227
1 vote
1 answer
68 views

If gaseous oxygen and dissolved oxygen (in water) have the same partial pressure, will they diffuse into solid materials at comparable rate?

To be specific, I am wondering about the dynamics of molecular oxygen diffusion into gas-permeable polymer materials, which is the sensing process of the optical oxygen probe (polymer-encapsulated ...
GradStudent_BME's user avatar
1 vote
1 answer
840 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 ...
user avatar
1 vote
1 answer
291 views

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 ...
uhoh's user avatar
  • 5,888
1 vote
1 answer
44 views

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 ...
Phil Rosenberg's user avatar
1 vote
1 answer
82 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 ...
math's user avatar
  • 43
1 vote
1 answer
276 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}}}...
mnulb's user avatar
  • 263
1 vote
1 answer
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{...
mnulb's user avatar
  • 263
1 vote
1 answer
56 views

Could the presence of multiple stabilizer oxides induce sluggish diffusion in a stabilized zirconia to increase lifetime?

The presence of yttria stabilizes zirconia's high temperature allotropes, but it also decreases the lifetime due to more defects that can induce more diffusion into yttria rich and poor regions, ...
user145034's user avatar