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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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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
3 votes
1 answer
63 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
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1 answer
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In steady state diffusion of atoms, does dJ/dt = 0 hold true?

My textbook says that under steady state flow the flux is independent of time and remains the same at any cross-sectional plane along the diffusion direction. Further, it gives the following ...
justakid's user avatar
3 votes
1 answer
153 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
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1 answer
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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
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1 answer
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How do I express concentration of a substance at the interface between two membranes of different diffusivities and lengths at steady state?

I am lost on this question from my textbook: "A solute diffuses across two membranes, A and B. The membranes' thickness are $\Delta x_A$ and $\Delta x_B$ respectively. The membranes' ...
Lim Min Kang's user avatar
1 vote
1 answer
65 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
5 votes
2 answers
500 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
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4 votes
2 answers
498 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
2 votes
2 answers
258 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
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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. ...
rdemyan's user avatar
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What happens to a solute's potential energy during diffusion?

I was thinking, if you have a large amount of water, with an uneven solute concentration, diffusion will lead to an even concentration of solute throughout the solution. Intuitively,that would mean ...
Eli's user avatar
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0 answers
37 views

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 ...
John M.'s user avatar
  • 111
1 vote
1 answer
113 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
0 answers
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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-...
Mowgli's user avatar
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0 answers
274 views

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\...
Jonny_92's user avatar
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-3 votes
2 answers
93 views

Why do different places on Earth have different concentrations of particulate matter in the atmosphere? [closed]

From the second law of thermodynamics, I would expect the pollutants to diffuse from a region of higher concentration to a region of lower concentration. The rates of diffusion in liquids and solids ...
Amogh's user avatar
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3 votes
0 answers
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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 ...
katara 's user avatar
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1 vote
1 answer
289 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
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4 votes
0 answers
71 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
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1 answer
105 views

Hydrogen Dispersion in room [closed]

I need to measure the concentrarion of pure hydrogen in a room caused by leakage or exhaust gases to evaluate the risk of ignition. Maybe there is some model available for indoor locations, similar to ...
Mark Houlen's user avatar
3 votes
1 answer
127 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
2 votes
1 answer
528 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
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0 answers
47 views

If I have an oil that contains an impurity that's more soluble in water than in oil, is there a way to "wash out" the impurity with water?

Maybe this question is better classified as "physics" than chemistry, but I'm trying it here. Suppose I'm concerned about a substance S that is highly soluble in water and less soluble in ...
James's user avatar
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1 vote
0 answers
31 views

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) ...
TLDR's user avatar
  • 143
3 votes
0 answers
626 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
2 votes
0 answers
353 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
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1 vote
0 answers
116 views

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/...
rdemyan's user avatar
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1 vote
0 answers
48 views

Hydrogen permeation from low to high absolute pressure area due to difference in partial pressure?

I need to get help with a question regarding hydrogen permeation which I do not really how to get around. The statement is as following: A steel container contains helium gas at high pressure (100 ...
QR-dance's user avatar
1 vote
0 answers
39 views

When is it realistic to model diffusion without advection?

Brownian motion abounds in nature, but so does drift current. In theoretical models of solutions and colloidal suspensions it is sometimes assumed that advection is negligible. I'm wondering if this ...
TLDR's user avatar
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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
0 votes
1 answer
267 views

Finding molar mass of uranium fluoride using Graham’s law of diffusion

Problem A sample of uranium fluoride is found to effuses at the rate of $\pu{17.7 mg/h}.$ Under comparable conditions, gaseous iodine effuses at the rate of $\pu{15.0 mg/h}.$ What is the molar mass ...
Alex's user avatar
  • 99
-1 votes
1 answer
441 views

What is the relation of water potential with gibbs free energy? [closed]

In my high school textbook, they have stated that diffusion is a process in which water moves along a free energy gradient. I cannot understand how water potential may be related to the Gibbs free ...
Sayak Roy's user avatar
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
0 votes
0 answers
48 views

real meaning of osmotic and turgor pressures

I am a high school student and I am very confused in how we define osmotic pressure? Osmotic pressure is defined as the pressure required to stop the diffusion of solvent into a solution by applying ...
Arun Bhardwaj's user avatar
0 votes
0 answers
20 views

Difference in collision cross-section obtained by measurement method

I have a simple question of Physical Chemistry, but I don't know the answer. We can find collision cross-section(σ) through experiments in three ways. first, diffusion flux experiment. diffusion ...
Jun's user avatar
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0 votes
1 answer
2k views

Permeability of containers to poop smells

I do a lot of hiking trips that involve driving for an hour or two to the trailhead in the predawn hours. I'm a morning pooper, so I need to poop during the drive. Before COVID, I would usually plan a ...
user avatar
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
0 answers
85 views

Is it easier to mix a solution that is in the liquid or in the vapor phase?

In the article on dilution, Wikipedia has the following statement: The same direct relationship applies to gases and vapors diluted in air for example. Although, thorough mixing of gases and vapors ...
Karsten's user avatar
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0 votes
1 answer
646 views

Whats the driving force behind simple diffusion? Is it just the count of molecules?

If I were to have two separate containers with solutions of different concentrations with a small opening, most of the molecules would flow down the concentration gradient. Does this occur just ...
Igor Bernát's user avatar
2 votes
2 answers
268 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
1 answer
140 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
0 votes
0 answers
59 views

Ratio of rates of diffusion of gases

I stumbled upon a question, A mixture of 50 mL of Hydrogen gas and 50mL of Oxygen gas is allowed to effuse through an effusimeter. After some time it is observed that the residual gas occupies 90mL. ...
Aryan Verma's user avatar
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
0 votes
0 answers
693 views

How long will it takes two miscible liquids to fully mix (homogenize) through diffusion?

This question occurred to me while I was pouring milk into my coffee and was too lazy to stir. Assume you have some volume $V_a$ of liquid A directly on top of another volume $V_b$ of liquid B. The ...
gardenhead'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
1 vote
0 answers
22 views

Algae Cultivation Using Polyethylene Film Reactor Vessel Floating In Pool with Algicidal ClO2 Concentration

I'm attempting to grow chlorella algae in a polyethylene film bag (which contains the growth medium) submerged in a temperature-moderating, above-ground swimming pool. This presents a challenge in ...
James Bowery'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
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0 votes
1 answer
562 views

What is the relative rate of diffusion of ammonia to hydrogen chloride, both in gaseous states? [closed]

I encountered this problem during an assignment: I answered it as C, but the assignment grader marked it as wrong and indicated that A is correct. I asked another instructor about it and gave me a ...
Omar Ibrahim Culé's user avatar
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