Questions tagged [adsorption]

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

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Order of reaction in adsorption process [on hold]

(1) $\ce{PH3-> P + 3/2 H2}$ Is the decomposition of phosphine on tungsten surface at low pressure is a pseudo first order reaction because this does not depend on the concentration of phosphine ...
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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 ...
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231 views

Is there a direct relationship between the adsorption energy and the catalytic activty

I have seen in several papers, where people correlate adsorption energy with the catalytic activity; the greater the adsorption energy, the greater would be the catalytic activity. I understand that ...
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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. ...
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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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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 ...
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2answers
171 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 ...
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Is it possible to reduce the desorption temperature of an adsorption/desorption reaction by changing (decreasing) the pressure?

I am studying about zeolite/water adsorption beds and need to see if there is a way to tune the desorption temperature. Ideally, I need to reduce the desorption temperature. Is it possible to do this ...
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256 views

What are molecular species?

I am a highschooler learning about adsorption for the first time.My school textbook says-- "The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is ...
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1answer
345 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 ...
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34 views

Preparation of Copper (II) Sulfate Pentahydrate Solution

how would you make a solution of Copper (II) Sulfate Pentahydrate to achieve 150, 200, 250 and 300 mgL−1 concentration of copper? I do not have the anhydrous version of the solute. Also, when I ...
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59 views

Why enthalpy of adsorption is negative?

I have already read Is adsorption exothermic, and if so, why? but it didn't answered my query. To illustrate, let's take a hypothetical vacuum space. In that space, there is a solid and a gas, the ...
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997 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 ...
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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_\...
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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 ...
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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 ...
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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 ...
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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 ...
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How to quantify the adsorption affinity of gases?

Is there a term/quantity which shows how 'sticky/adsorptive' a molecule is? I am interested in gas adsorption on steel surfaces in our mass spectrometer and would like to estimate which gases have a ...
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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 ...
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Hygroscopic Substances and Drying Agents

My book says: Most of the hygroscopic substances are drying agents Based on what I read on several websites, I think dehydrating agents also act as drying agents. If so, all dehydrating agents ...
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Aren't “lack of specificity” and “nature of adsorbate” contradictory factors in physisorption?

It was mentioned in my course book under "Characteristics of physisorption" that: Lack of specificity: An adsorbent does not show any preference for a particular gas as the van der Waal's ...
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218 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 ...
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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 ...
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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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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) ...
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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 ...
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Application of BET to micropore

'application of the BET equation should be restricted to the range where the term n(1 – p/p0) continuously increases with p/p0'see 5.2.2 in the reference This is one of the criterias IUPAC proposes ...
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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 ...
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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 $\...
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188 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+ > ...
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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 ...
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1answer
106 views

Langmuir method

I have done a biosorption study using a protein as a biosorbent and six different concentrations of $\ce{Pb}$ ions. I need to show the efficiency of the biosorbent, I was told to use the Langmuir ...
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2answers
264 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{...
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1answer
531 views

“Nitrogen (gas) is physisorbed over iron (metal) at room temperature”: Is this for real? [closed]

My copy (PDF) of Levine's Physical Chemistry (6th ed.), page 570-571, section: "Adsorption of Gases on Solids", states: Physical adsorption is nonspecific. For example, $\ce{N2}$ will be physically ...
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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 ...
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2answers
241 views

What is the physical state of the gas adsorbed on a solid adsorbent?

I am studying surface chemistry in high school I have this doubt and I am unable to find a answer your help is appreciated I searched for the answer on google I asked my chemistry teacher he said the ...
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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 ...
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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, ...
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Can negative adsorption be considered equal to sorption?

In my book it was written sorption is basically when the substance gets uniformly distributed into the bulk of the solid but at the same time its concentration is higher at the surface then in the ...
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870 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 ...
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477 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 ...
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797 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 ...
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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: ...
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1answer
124 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 ...
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116 views

How does physical adsorption of mixed gas occur on solid? (eg I mean how the gas molecules of compete each other for a slot on solid surface)

I am working on sorption phenomenon of gases (including inert gas) on coal seam surface. For a mixture of 2 gases at a certain pressure, carbon dioxide and methane, for instance, $\ce{CO2}$ is ...
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1answer
47 views

How to convert the D'Arcy and Watt model from activity to concentration in mol/m^3

The D'Arcy and Watt 1970 model in "Analysis of sorption isotherms of non-homogeneous sorbents" for water adsorption is as follows: $$W = \frac{KK'a}{1+Ka} + ca + \frac{kk'a}{1-ka},$$ where: $W$ is ...
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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 ...
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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? ...
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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 ...