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Is adsorption exothermic, and if so, why?

There are two common arguments presented as for why $\Delta H < 0$: Argument (1): Well, indeed I see nothing wrong with the argument presented by the textbook. If adsorption takes place ...
getafix's user avatar
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10 votes

Why are van der Waals' forces between gas molecules strong near its critical temperature?

Critical temperature is kind of measure of the strength of intermolecular van der Waals force. Comparison of actual and critical temperature is kind of comparison of average kinetic energy of ...
Poutnik's user avatar
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8 votes
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Catalysist activation energy - the Brønsted-Evans-Polanyi relation

First, a note on the Bell-Evans-Polanyi (BEP) equation: The form you've written it in disguises what the constant $\alpha$ tells you. From the wikipedia article, it's said that $\alpha$ is a number ...
jheindel's user avatar
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8 votes

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

The IUPAC defintion isn't more limited than the ones you've read. Instead, it is more general. Your confusion results from not being familiar with the term "condensed phase". You think a ...
theorist's user avatar
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6 votes
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Is the rate of desorption dependent on pressure?

Without knowing exactly what you were told its hard to be exact, but here is a description of the situation. The Langmuir model makes assumptions (a) adsorption is complete when the surface is filled ...
porphyrin's user avatar
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6 votes
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How does water freeze and crystallize on a cold superhydrophobic surface?

As acknowledged in your question, there are a large number of factors at play here. The most basic of these is that there are three fundamental mechanisms by which freezing of a droplet can initiate ...
airhuff's user avatar
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5 votes
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How does activated carbon trap impurities?

Never forget to interpret in terms of physical/chemical forces, by order of energy: van der Waals, hydrophobic (pseudo forces), hydrogen bonds, disulfide bridges, covalent, electrostatic (for the most ...
user50565's user avatar
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Why does the BET equation take into consideration a multimolecular-layer, even though it deals with chemisorption?

Brunauer–Emmett–Teller (BET) explains the physical adsorption of gas molecules on a solid surface, and doesn't address chemisorption. Even the wikipedia link that you provided, makes that quite ...
getafix's user avatar
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5 votes
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Why does Freundlich adsorption isotherm not have a term for surface area?

The ratio $$\frac{x}{m}= k P ^{1/n}$$ can be re-expressed in terms of the area $A$, surface-to-volume ratio $\lambda$, and density $\rho$ (note that $m=A\rho/\lambda)$: $$\frac{x}{A}= k' P ^{1/n}$$...
Buck Thorn's user avatar
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4 votes
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Effect of pressure on adsorption of a gas

Short Answer The following equilibrium roughly represents what goes on during physisorption of a gases onto a a surface. $$\ce{Gas + Surface <=>[adsorption][desorption] Gas--Surface} $$ The ...
getafix's user avatar
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4 votes
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Is it possible for the forward and reverse reactions to have different reaction orders?

Why is this strange? Consider: $$\ce{2A <=>[$k_1$][$k_{-1}$] A_2}$$ Forward rate is second order: $k_1[\ce{A}]^{2}$. Reverse rate is first order $k_{-1}[\ce{A2}]$.
Zhe's user avatar
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4 votes
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What is the physical state of the gas adsorbed on a solid adsorbent?

Well, it usually depends on the temperature: if temperature is too low, molecules cannot move so freely so they are localized on top of the solid without much movement. However, in general cases the ...
Nando's user avatar
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4 votes
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Calculating surface area from BET results

Your problem is not the unit conversion, but the units you have used. The adsorption cross-section of $\ce{N2}$ ($s$) has been found using BET method is $\pu{0.162 nm^2}$ (Langmuir). Yet, you have ...
Mathew Mahindaratne's user avatar
4 votes
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Finding the Freundlich adsorption isotherm from the graph of log(x/m) v/s log(p)

One version of Freundlich adsorption isotherm equation is: $$ \frac xm = Kp^{\frac12}, $$ which can also be written as: $$ \log \frac xm = \log K + \frac12\log p $$ This is a straight line equation of ...
Mathew Mahindaratne's user avatar
3 votes
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Freundlich Equation's dimensions

Technically speaking, one typically wouldn't write the left hand side unitless, as it is the ratio of the mass of two different components (usually mg of some chemical per gram of the surface). But, ...
Tyberius's user avatar
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3 votes

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

My book (G. Wedler, H.-J. Freund, Lehrbuch der Physikalischen Chemie, 6. Edition ... obviously a German book on physical chemistry) begins with the following, when introducing the BET equation. ...
pH13 - Yet another Philipp's user avatar
3 votes
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Plotting a Langmuir adsorption isotherm

Self Answer Additionally, I plotted $\frac{1}{V}$ and $\frac{1}{p}$, as suggested by @Chester Miller in the comments below, and indeed I get a straight line. A linear model fit was performed and ...
getafix's user avatar
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3 votes

How does adsorption work?

On colliding with a surface the molecules do not necessarily bounce off because, depending on the collision energy, Van-der-Waals forces can act to hold the gas molecule close to the surface. These ...
porphyrin's user avatar
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3 votes

How does adsorption work?

Adsorption (with a d) is caused by intermolecular Van der Waals Forces allowing molecules to stick to a solid surface. The solid surface can be described using a Langmiur model. In this model a ...
Agriculturist's user avatar
3 votes

What is 'desorption hysteresis'?

Hysteresis occurs when the state of the system depends on its past states---that is, the state of the system is memory-dependent. The canonical example is a ferromagnet: if you apply and slowly ramp ...
a-cyclohexane-molecule's user avatar
3 votes
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Hygroscopic Substances and Drying Agents

Read closer: Most of the hygroscopic substances are drying agents not all drying agents are hygroscopic substances. First Terminology: Hygroscopic: Absorbs water from air Drying agent: ...
A.K.'s user avatar
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3 votes

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

The mechanism(s) of iodine adsorption into carbons are complex and strongly dependent on each carbon. That is, iodine can be physisorbed in the carbon micro/mesopores, but in carbons with a rich ...
Nando's user avatar
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3 votes

Why enthalpy of adsorption is negative?

I will point out another equation: $$\mathrm{d}G = \mathrm{d}H - T\,\mathrm{d}S$$ For adsorption $\mathrm{d}S<0$, as molecules go more organized. Therefore also $\mathrm{d}H < 0$ must be ...
Poutnik's user avatar
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3 votes
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Dangers of using activated carbon past its lifespan

Every adsorbent has a saturation capacity depending on its active surface area. The idea to replace carbon filter is not only due to the saturation capacity but imagine fungi, bacteria may be adsorbed ...
AChem's user avatar
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3 votes

Is activated charcoal an air purifier?

Agreed: unless air is pushed through the activated charcoal bed, few impurities would be adsorbed. It would depend on how tightly the substance clings to the carbon, i.e. it would vary with impurity, ...
DrMoishe Pippik's user avatar
3 votes
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Is there a practical re-use value gained by grinding up activated carbon that is spent/saturated?

No. Grinding activated carbon will not change anything relevant. The reason is because surface area does not have an effective influence on the usefulness of activated carbon. Activated carbon is ...
Maurice's user avatar
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3 votes
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Is the line between physisorption and chemisorption species specific?

Take it as a conventional rule of thumb. If desorption enthalpy is not bigger than evaporation enthalpy, we can assume the cohesion forces of adsorbed molecules between each other and with the surface ...
Poutnik's user avatar
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2 votes

Does glass adsorb methanol to an exceptional extent?

Exceptional is subjective term, and can't be responded to sensibly. But more/less can be discussed. This is somewhat complex. The isotherm is an equilibrium between adsorption and desorption. ...
Lighthart's user avatar
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2 votes
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Counterions in adsorption of ions

Since this got no answers, I'm posting an answer from Reddit user midnight-cheeseater, which can be found here. There are two main possibilities here, depending on how the ions are adsorbed: ...
Marcel's user avatar
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