Questions tagged [diffusion]

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

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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 ...
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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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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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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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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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25 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 ...
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36 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 ...
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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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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 ...
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72 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 ...
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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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23 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 ...
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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 ...
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253 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 ...
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1answer
29 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 ...
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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 ...
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240 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 ...
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2answers
74 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 ...
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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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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. ...
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85 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 ...
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69 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 ...
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1answer
58 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 ...
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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 ...
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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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190 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 ...
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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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1answer
46 views

Electrochemistry - Understanding Diffusion Potential

I have a big problem trying to wrap my head around this for several hours and I cannot seem to make sense of it. I have to link this scheme with the 3 colored potential profiles on the bottom of the ...
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824 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 ...
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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 ...
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45 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 ...
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42 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 ...
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1answer
136 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 ...
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252 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....
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405 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 ...
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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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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 ...
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225 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 ...
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143 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 ...
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53 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 ...
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1k 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 ...
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41 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 ...
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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 ...
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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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415 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 ...
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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 ...
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657 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 ...
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366 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) ...
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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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564 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 ...