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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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15
votes
4answers
716 views

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? ...
14
votes
5answers
20k views

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 ...
13
votes
1answer
798 views

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 ...
12
votes
1answer
6k views

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 &...
9
votes
6answers
8k views

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 ...
8
votes
1answer
998 views

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 ...
8
votes
1answer
3k views

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_\...
8
votes
0answers
141 views

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 ...
7
votes
1answer
579 views

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 ...
6
votes
1answer
286 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 ...
6
votes
1answer
78 views

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 ...
6
votes
1answer
479 views

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 ...
6
votes
1answer
2k views

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 ...
6
votes
1answer
269 views

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 ...
5
votes
1answer
63 views

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 $\...
5
votes
0answers
871 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 ...
4
votes
1answer
125 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 ...
4
votes
1answer
27k 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: ...
4
votes
2answers
2k 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)...
4
votes
1answer
385 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: $ \...
4
votes
1answer
139 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 ...
4
votes
0answers
43 views

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 ...
4
votes
0answers
394 views

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 ...
3
votes
1answer
3k views

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 ...
3
votes
1answer
103 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 ...
3
votes
1answer
6k 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) ...
3
votes
1answer
383 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 ...
3
votes
2answers
91 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 ...
3
votes
2answers
4k views

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. ...
3
votes
4answers
4k 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) ...
3
votes
3answers
1k 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 ...
3
votes
1answer
141 views

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 ...
3
votes
0answers
189 views

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+ > ...
2
votes
2answers
266 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{...
2
votes
1answer
549 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 ...
2
votes
1answer
4k 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?
2
votes
1answer
219 views

What is 'desorption hysteresis'?

I am currently reading a paper titled "Polystyrene Nanoplastics-Enhanced Contaminant Transport: Role of Irreversible Adsorption in Glassy Polymeric Domain" (link here). In the paper, the authors ...
2
votes
1answer
2k views

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, ...
2
votes
1answer
347 views

Does glass adsorb methanol to an exceptional extent?

Does (borosilicate) glass adsorb methanol to an exceptional extent? We are doing vapor density measurements of organic solvents using a microbalance and a sealed glass sphere. Other polar molecules ...
2
votes
1answer
337 views

Adsorption on surface of adsorbent

Why is energy released during the process of adsorption? How is this energy change observed and how is it calculated?
2
votes
1answer
611 views

Spices are absorbed or adsorbed in food?

When we cook food, we add several spices and condiments which enhance color, taste and smell. Are these spices and condiments just adsorbed on the food particles? Or are they absorbed? For example ...
2
votes
0answers
71 views

How did Zyklon hold and release HCN?

$\ce{HCN}$ is notoriously unstable: It boils at room temperature, and it tends to polymerize when concentrated in unbuffered liquid form. Yet $\ce{HCN}$ was for decades widely used as a fumigant ...
2
votes
0answers
262 views

Why does physisorption change to chemisorption at high temperatures?

I read in my textbook: In certain cases, physisorption changes to chemisorption as temperature is increased. Could anyone explain why it is so? I know the basics of both physisorption and ...
2
votes
0answers
185 views

How to develop a Reactive Force Field (ReaxFF)? (Molecular simulation)

Currently, I am working on CO2 capture on Hydrotalcites as solid adsorbents. I want to run molecular simulations to analyse the behaviour of the material under different temperatures, pressures and ...
2
votes
0answers
44 views

Langmuir parameters for fixed bed continous column

I have prepared a model of fixed bed adsorption column in MATLAB. I have to insert Langmuir parameter value there, so how can I calculate them in case of continuous fixed bed column. I have calculated ...
2
votes
0answers
55 views

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 ...
2
votes
0answers
2k views

Why increase in enthalpy leads to increase in entropy? [closed]

Given statement: Enthalpy of adsorption is the strength at which molecule (say $\ce{H2}$) is bound to the adsorbent (say some metal center). For a free $\ce{H2}$ molecule, the entropy contribution is ...
2
votes
0answers
264 views

Why we have mass of adsorbent in Freundlich equation?

In Freundlich equation why we have $m$ the mass of adsorbent. I mean it is surface chemistry and on the surface of adsorbent the adsorption takes place so why we have mass of adsorbent in that ...
2
votes
0answers
56 views

Chemical bond of adsorbed atoms

When oxygen is adsorbed on iron metallic surface, does it create $\ce{Fe-O}$ bonds like the one in iron oxide? Can it be considered as a monolayer of iron oxide on the surface? If not, how is the ...
1
vote
2answers
3k 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. ...