Questions tagged [diffusion]

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

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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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28 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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16 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 ...
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18 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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12 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 ...
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1answer
105 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
28 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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36 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 ...
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1answer
123 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
59 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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1answer
29 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 ...
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31 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. ...
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1answer
82 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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32 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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19 views

What is the binding speed of coated Fe3O4 nanoparticles to microparticles diffused in water?

Does someone know how to determine the binding speed of $\ce{Fe3O4}$ nanoparticles coated with the alkyl chain of hexadecyltrimethoxysilane to microparticles in water? I know that a precise answer is ...
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1answer
45 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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16 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 ...
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1answer
34 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 ...
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1answer
136 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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34 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 ...
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1answer
43 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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1answer
501 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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34 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 ...
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43 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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39 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
134 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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216 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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2answers
373 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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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?
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111 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 ...
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203 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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1answer
122 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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1answer
48 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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1answer
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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1answer
40 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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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 ...
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1answer
741 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)....
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1answer
360 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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74 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 ...
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1answer
566 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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1answer
300 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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43 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 ...
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522 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 ...
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2answers
976 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 ...
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143 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 ...
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2answers
103 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 $\...
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2answers
100 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 ...
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2answers
334 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 ...
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4answers
8k 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/...
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147 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}}}...