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Questions tagged [adsorption]

The adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.

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Why is Charcoal such an excellent adsorbent?

Charcoal (also activated charcoal) is known to adsorb a huge variety of substances including a variety of paints, dyes and many different kinds of ions. Moreover, the amount of adsorption at normal ...
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Relative strength of desiccants

Is it meaningful to characterize the relative strength of desiccants? For example, is there a measure of hygroscopy, or an ordering of desiccants, such that higher ones will always dry lower ones? ...
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13 votes
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Reaction mechanism in fluoride adsorption to aluminum oxide

Despite a fair amount of research (excluding non-open access journals, to which I have not got access), I cannot seem to find an explanation of the process that takes place when $\ce{F^-}$ adsorbs to ...
Marcel's user avatar
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12 votes
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Is adsorption exothermic, and if so, why?

Why is adsorption exothermic? The explanation given in my textbook is: For a process to be spontaneous, the thermodynamic requirement is that, at constant temperature and pressure, $\Delta G &...
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10 votes
6 answers
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Why does chemisorption increase with rise in temperature, even though it is an exothermic process?

Chemisorption is exothermic process, but still it increases with increase in temperature. Why? I know that there needs to be a minimum activation energy to be achieved in order to initiate ...
MrObjectOriented's user avatar
8 votes
1 answer
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Why are van der Waals' forces between gas molecules strong near its critical temperature?

My textbook says …easily liquefiable gases i.e. with higher critical temperatures are readily adsorbed as van der Waals' forces are stronger near the critical temperatures. What I do understand is ...
AdityaS's user avatar
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Catalysist activation energy - the Brønsted-Evans-Polanyi relation

I have stumbled upon something called the Brønsted-Evans-Polanyi relation in a study about the design of catalysts (for reactions like those in hydrocracking fuel production.) The relation shows that ...
Steeven's user avatar
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Plotting a Langmuir adsorption isotherm

We have, $$\theta = \frac{Kp_\mathrm a}{1+Kp_\mathrm a}$$ where, the fractional coverage $\theta$ is defined as the number of sites occupied by adsorbate $A$ over the total number of sites. $p_\...
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8 votes
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New finding in cobalt compound that absorbs oxygen - is it really a breakthrough?

Very recently Chemical Sciences published results of the discovery of a new cobalt compound that can absorb oxygen at presumably a higher capacity than what has been achievable before. The paper is ...
docscience's user avatar
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7 votes
1 answer
399 views

Kinetics of interstellar chemistry: Applying steady state to formation of H₂

I am trying to solve problem 2 from the 2009 International Chemistry Olympiad (IChO), which is as follows: If two atoms collide in interstellar space the energy of the resulting molecule is so ...
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7 votes
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How does activated carbon trap impurities?

I've tried and I've tried to find an answer to this all over the web, but I can't seem to find an in depth explanation. To the best of my knowledge, activated carbon has a very microporous structure ...
Charlie's user avatar
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Chemical reactions involved in staining

I'm a geology student completing a project on chemical staining and was after some chemistry help on some of the reactions taking place. I am using various different stains to identify carbonate and ...
Matt's user avatar
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1 answer
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Why does Freundlich adsorption isotherm not have a term for surface area?

Why does Freundlich adsorption isotherm not have a term for surface area? The formula given by Freundlich adsorption isotherm: $$ \frac{x}{m}= k P ^{1/n}$$ Where $x$ is the mass of gas adsorbed ...
Mr.HiggsBoson's user avatar
6 votes
1 answer
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Why is Cyclodextrin cavity hydrophobic?

Actually this is going to be a list of interconnected questions. Please bear with me. Wikipedia article on cyclodextrin (CD) says that it is hydrophobic from inside. (1) How is it hydrophobic when ...
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Interaction between a pencil and rubber (eraser)

Is there a interaction between a graphite pencil and and a eraser. For example, if I drew a line on a piece of paper and then erased that, what interaction is occurring? Is it a Van der Waals ...
MattB's user avatar
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0 answers
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Do "pseudo Van der Waals" gases exist?

In college, when deriving the Langmuir isotherm for gas-solid adsorption, the professor proposed a modified version of the Van der Waals state equation, what he called the "pseudo Van der Waals ...
David Moldes's user avatar
6 votes
0 answers
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Why is there preferential adsorption of a common ion during preparation of colloids by peptization?

There was a similar question asked here on Chem SE, but the answer was not very satisfactory to me, so I am asking a fresh question. Peptization is the process of creating a colloid from a precipitate ...
Samardeep singh's user avatar
5 votes
2 answers
11k views

Dangers of using activated carbon past its lifespan

Activated carbon (AC) is one of the most widely used media for water filtration. It's effective at removing chlorine taste and odor, and it's recognized as being safe. However, most activated carbon ...
N4v's user avatar
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1 answer
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Calculating surface area from BET results

I have been trying to work out the workings of the BET method and I have come to a standstill. The surface area of a sample is given by $$ S_{\text{BET}} = \frac{\nu_{\text{m}}Ns}{V} $$ where $\...
Francisco's user avatar
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1 answer
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Why does the order of adsorption of hydrated alkali metals on an ion exchange resin decrease down the group?

Why does the order of adsorption of hydrated alkali metals on an ion exchange resin decrease down the group? I recently did a question on this topic and they say adsorption order is $$\ce{ Li+ > ...
Nihal N.L's user avatar
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Equations Used in Isothermal Titration Calorimetry

I have been attempting to understand and derive the formulas used for ITC which can be found here starting on page 310. I am particularly interested in the single set of identical sites. To first ...
MasterYoda's user avatar
5 votes
0 answers
1k views

Selective sorption of toxins by polymethylsiloxane polyhydrate

Polymethylsiloxane polyhydrate (PMSPH) is used as enterosorbent for a couple of decades (nowadays under the trademark "Enterosgel"), intended for binding in the gastrointestinal tract and excretion of ...
andselisk's user avatar
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Difference between neutral and basic activated alumina

Sigma Aldrich sells two different types of activated alumina for column chromatography: neutral and basic. Apparently basic alumina is more active and better at adsorbing anions. Why is this the ...
Marcel's user avatar
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4 votes
1 answer
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Does adsorption violate thermodynamics?

My textbook reads as follows: When a gas is adsorbed, the freedom of movement of its molecules become restricted. This amounts to decrease in the entropy of the gas after adsorption, i.e. Entropy ...
Abdullah's user avatar
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4 votes
2 answers
273 views

Why is the IUPAC definition of adsorption so different from other definitions?

NB: This question has been edited. Originally, some of the confusion was caused by me not knowing that condensed phase could refer to solid phases as well. This has been removed, but the confusion ...
user110391's user avatar
4 votes
1 answer
214 views

How does water freeze and crystallize on a cold superhydrophobic surface?

Superhydrophobic surfaces are nano-structured to "repel" liquid water and there has been a lot of work done to understand the microscopics of wetting of these nanostructures. What I currently am ...
user157879's user avatar
4 votes
1 answer
637 views

Does adsorption occur between liquids?

While reading a paper in a field other than chemistry, the author mentions a phenomena that he labelled "adsorption" and describes it as follows: ...I am told (though I do not know which liquids ...
Dennis's user avatar
  • 253
4 votes
1 answer
35k views

How to determine Langmuir adsorption isotherm constants and use the models

I am doing some adsorption tests on bio materials and would like to test the data with Langmuir and Freundlich adsorption isotherm models. Assume these values: ...
user7091's user avatar
4 votes
2 answers
3k views

How does activated carbon bind the adsorbate?

I read some articles and journals about activated carbon and found a problem about how the adsorbate could bind to the activated carbon. Some said it is because of intramolecular forces (van der Waals)...
innayk's user avatar
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2 answers
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Freundlich Equation's dimensions

So, we have the Freundlich's Isotherm equation as $\frac{x}{m} = kp^{\frac{1}n}$, where the LHS measures the extent of adsorption with the corresponding pressure $p$ in the RHS with the two constants, ...
vs_292's user avatar
  • 149
4 votes
1 answer
533 views

Counterions in adsorption of ions

When an ion is adsorbed from an aqueous solution onto a solid, what happens to its counterion? Obviously, the solution does not become charged - does this mean that it too is adsorbed? (Example: $ \...
Marcel's user avatar
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4 votes
1 answer
185 views

Soil-solution cations in competition for exchange sites

How could one determine the likelihood of one cation displacing another on a negatively charged exchange site of a clay particle? For example, in a soil solution containing equal parts (by number of ...
Randy's user avatar
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4 votes
1 answer
255 views

Understanding isosteric enthalpy (heat) of adsorption

I am trying to understand what is isosteric heat of adsorption. Based on van't Hoff equation: $$ \left(\frac{\partial \ln K}{\partial T}\right)_θ = \frac{ΔH^\circ}{RT^2} $$ and $ΔH^\circ$ is defined ...
Anton's user avatar
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4 votes
0 answers
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Pd-catalysed hydrogenation of imines

Hydrogenation of imines to amines by $\ce{H2}$ on $\ce{Pd/C}$ has been used e.g. in the synthesis of Pumiliotoxin. By contrast, carbonyl groups are rarely reduced in this way, which I though was due ...
GingerBadger's user avatar
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3 votes
1 answer
118 views

Can there be active THC be trapped in the evaporator?

In relation to the vaporization of THC, when smoked, is it possible that there is any active THC residue that becomes trapped inside the evaporator after the flame goes out? Wouldn't some of the ...
ZEM's user avatar
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3 votes
3 answers
3k views

Is the rate of desorption dependent on pressure?

While I was learning about Langmuir's adsorption isotherm in my chemistry class, my teacher talked about the situation when the rate of adsorption and desorption will become equal. However, he ...
EdmDroid's user avatar
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3 votes
2 answers
394 views

Is the adsorption of dissolved iodine onto activated carbon physical adsorption or chemical adsorption?

For an experiment, I am looking to see the effect of temperatures from 0–100 °C on the efficacy of activated carbon as an adsorbent. My adsorbate is iodine and I am confused as to whether the ...
Anonymous Chemistry Student's user avatar
3 votes
1 answer
8k views

Effect of pressure on adsorption of a gas

I am currently studying about the basic terms of surface chemistry, and am facing some conceptual doubt regarding the following: What effect does pressure have on the adsorption of a gas (adsorbate) ...
Pink's user avatar
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3 votes
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What is the difference between BET and Langmuir model for calculating the specific surface area?

Brunauer–Emmett–Teller (BET) surface area is measured by specific surface area of the adsorbent. BET surface area is measured by using non-corrosive gases like $\ce{N2}$, $\ce{CO2}$, $\ce{Ar}$ etc. ...
JaafarMehrez's user avatar
3 votes
4 answers
8k views

Why does physisorption (physical adsorption) increase with ease of liquefaction?

This is what my textbook says about physisorption The amount of gas adsorbed by a solid depends on the nature of gas. In general easily liquefiable gases (i.e. with higher critical temperature) ...
Raghav's user avatar
  • 248
3 votes
3 answers
4k views

Why Freundlich adsorption isotherms fails at high pressure conditions?

Experimentally it was determined that extent of gas adsorption varies directly with pressure, and then it directly varies with pressure raised to the power 1/n until saturation pressure Ps is reached. ...
Grace's user avatar
  • 460
3 votes
1 answer
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What is the direction of charge transfer between Aluminum and aliphatic amines physisorbed on top?

Is there dipole formation upon physisorption of an aliphatic amine to an aluminum substrate? What is the charge transfer direction? What if the aluminum substrate is clean, surface oxidized or covered ...
Zhanhao Hu's user avatar
3 votes
0 answers
660 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
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3 votes
0 answers
1k views

Order of reaction in adsorption process

(1) $\ce{PH3(g) <=>[W]PH3(adsorption)->[W]P(s) + 3/2 H2(g)}$ The decomposition of phosphine on tungsten surface at low pressure is a pseudo first order reaction. This is because the rate of ...
Apurvium's user avatar
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2 votes
2 answers
504 views

Why does the BET equation take into consideration a multimolecular-layer, even though it deals with chemisorption?

I came across the Brunauer-Emmet-Teller (BET) equation recently, and one thing that I found strange was an implicit reference to the formation of molecular multi-layer. In the BET equation $$ \begin{...
paracetamol's user avatar
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2 votes
2 answers
4k views

How does adsorption work?

I would like to know how adsorption works particularly between a gas and a solid. I know that there is an attraction of intermolecular forces between the gas molecules and the solid surface molecules. ...
ergon's user avatar
  • 259
2 votes
1 answer
1k views

Is it possible for the forward and reverse reactions to have different reaction orders?

For example, in the case of non-dissociative adsorption, the rate of the forward process is given by $$\frac{\mathrm{d}\theta}{\mathrm{d}t} = kCN(1−\theta)$$ where $C$ is the concentration, $N$ is ...
Marcel's user avatar
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2 votes
1 answer
5k views

What makes charcoal a good adsorbent to organic and non polar substances while alumina and silica are best for polar substances?

My question is, what makes charcoal a good adsorbent to organic and non polar substances while alumina and silica are best for polar substances?
Mae Manansala's user avatar
2 votes
1 answer
104 views

Is the line between physisorption and chemisorption species specific?

I was studying about heterogenous catalysis, and my Professor said something along the line, "When the adsorption energy is comparable to (or lower than) heat of evaporation, then it is ...
Tensor's user avatar
  • 283
2 votes
1 answer
91 views

Is there a practical re-use value gained by grinding up activated carbon that is spent/saturated?

I want to buy bulk activated carbon for use in a DIY air-filtration set-up, like this, to improve air quality in my bedroom. From what I understand, the relatively larger sizes of carbon media on the ...
Mark K's user avatar
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