Q: Why is adsorption always exothermic?

\$Explanation:\$ The surface particle of any substance is active. They try to adsorb other molecules/atoms on it to become stable. When molecule/atoms get adsorb on the surface of the adsorbent, it becomes stable and releases energy. During adsorption, energy is released due to the presence of attraction between adsorbate and adsorbent molecules. Therefore, adsorption is always exothermic.

Q: According to Freundlich adsorption isotherm, which of the following is correct?

Correct Option : \$D\$Hint: Apply the concept that the adsorption isotherm given by Freundlich depends on the amount of pressure and changes accordingly.Explanation:According to Freundlich’s adsorption isotherm,\$\dfrac{x}{m}\propto p^{\dfrac{1}{n}}\$, where \$n>1\$.Here, \$p\$ is the pressure at equilibrium and \$\dfrac{x}{m}\$ is the mass of gas adsorbed per unit mass of the adsorbent substance.Let us have a look at the three situations.Case I: At low pressure, the formula can be written as:\$\dfrac{x}{m}=Kp\$ (where, \$K\$ is an arbitrary constant)Case II: At high pressure,\$\dfrac{x}{m}\$ becomes almost constant and reaches its saturation value.\$\dfrac{x}{m}=K\$ Case III: At intermediate range of pressure,\$\dfrac{x}{m}\$will depend mostly on the power of pressure which lies between \$0\$ and \$1\$ and is expressed as: \$\dfrac{x}{m}=K.p^{\dfrac{1}{n}}\$Hence, all three options are used in Freundlich's adsorption isotherm. Correct Option: \$D\$

Q: Adsorption of a gas follows Freundlich adsorption isotherm \$x\$ is the mass of the gas adsorbed on mass \$m\$ of the adsorbent. The plot of log \$\dfrac{x}{m}\$ versus log \$p\$ is shown in the given graph. \$\dfrac{x}{m}\$ is proportional to :

Solution:- (C) \${p}^{{2}/{3}}\$\$\dfrac{x}{m}=K.p^{1/n}\$\$\therefore log \dfrac{x}{m}=log K+\dfrac{1}{n}. log P\$slope \$=\dfrac{1}{n}=\dfrac{2}{3}\$\$\therefore \dfrac{x}{m}=K.p^{2/3}\$

Question 1

What is an adsorption isotherm? Describe Freundlich adsorption isotherm?

Accepted Answer

Adsorption isotherm is the variation of the mass of the gas (adsorbate) adsorbed per gram of the adsorbent with pressure at constant temperature.The Freundlich adsorption isotherm is the mathematical representation for the variation of the extent of adsorption ($x/m$) with pressure ($P$) at a given temperature. Here, $x$ is the mass of adsorbate and $m$ is the mass of adsorbent. The expression is $\displaystyle \dfrac {x}{m} =k\times P^{\dfrac {1}{n}}$,

Question 2

Why does physisorption decrease with the increase of temperature?

Accepted Answer

Physisorption is exothermic in nature. Therefore in accordance with the Le-Chatelier principle, it decreases with an increase in temperature. This means physisorption occurs at a low temperature more readily.Physisorption is reversible in nature.

Question 3

Why is adsorption always exothermic?

Accepted Answer

$Explanation:$ The surface particle of any substance is active. They try to adsorb other molecules/atoms on it to become stable. When molecule/atoms get adsorb on the surface of the adsorbent, it becomes stable and releases energy. During adsorption, energy is released due to the presence of attraction between adsorbate and adsorbent molecules.  Therefore, adsorption is always exothermic.

Question 4

What is the difference between physisorption and chemisorption?

Accepted Answer

Physisorption (Physical adsorption)Chemisorption (Chemical adsorption) Weak van der Waals forces are present between the adsorbate molecules and the adsorbent.Strong chemical forces similar to chemical bonds are present between the adsorbate molecules and the adsorbent.The enthalpy of adsorption is low (20 to 40 kJ/mol).The enthalpy of adsorption is high (40 to 400 kJ/mol). Occurs at low temperature and decreases with an increase in temperature. Occurs at high temperature and increases with increase in temperature.  It is reversible.It is irreversible. No significant activation energy is required.Usually, high activation energy is required. It forms multimolecular layers.It forms unimolecular layers.

Question 5

According to Freundlich adsorption isotherm, which of the following is correct?

Accepted Answer

Correct Option : $D$Hint: Apply the&#10;concept that the adsorption isotherm given by Freundlich depends on the amount&#10;of pressure and changes accordingly.Explanation:According to&#10;Freundlich&#8217;s adsorption isotherm,$\dfrac{x}{m}\propto&#10;p^{\dfrac{1}{n}}$, where $n>1$.Here, $p$ is the&#10;pressure at equilibrium and $\dfrac{x}{m}$ is the mass of gas adsorbed per unit&#10;mass of the adsorbent substance.Let us have a look at the three situations.Case I: At low&#10;pressure, the formula can be written as:$\dfrac{x}{m}=Kp$ (where, $K$ is an arbitrary constant)Case II: At high&#10;pressure,$\dfrac{x}{m}$ becomes almost constant and reaches its&#10;saturation value.$\dfrac{x}{m}=K$ Case III: At intermediate&#10;range of pressure,$\dfrac{x}{m}$will depend mostly on the power of&#10;pressure which lies between $0$ and $1$ and is expressed as:&#10; $\dfrac{x}{m}=K.p^{\dfrac{1}{n}}$Hence, all three&#10;options are used in Freundlich's adsorption isotherm.&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;&#10;Correct Option: $D$

Question 6

Distinguish between chemical and physical adsorption.

Accepted Answer

Physical adsorptionChemical adsorption  Weak van der Waals forces are present between adsorbate and adsorbent.Strong chemical (covalent) bonds are formed between   adsorbate and adsorbent. It has low heat of adsorption (20 to 40 kJ/mol). It has high heat of adsorption (40 to 200 kJ/mol).  Multilayers of adsorbed particles are formed.Monolayer of adsorbed particles  is formed.  It is not specific in nature.  It is specific in nature.

Question 7

Which of the following is not characteristic of chemisorption?

Accepted Answer

Chemisorption is a kind of adsorption which involves a chemical reaction between the surface and the adsorbate. New chemical bonds are generated at the adsorbent surface.Various characteristics of Chemisorption are-High specificity: Chemisorption is highly specific and it will only occur if there is some possibility of chemical bonding between adsorbent and adsorbate.It is irreversible in nature.Surface area: Chemisorption increases with the increase of the surface area of the adsorbent.Enthalpy of adsorption: Enthalpy of chemisorption is high ($80-240 $$kJ$ $mol^{-1}$)) as it involves chemical bond formation.Chemisorption doesn't form multimolecular layers and hence option D is a correct answer.

Question 8

The plot of$\log x/m$ against $\log p$ is a straight line inclined at an angle of $45^{\circ}$. When the pressure is $0.5\ atm$ and Freundlich parameter, $k$ is $10$, the amount of solute adsorbed per gram of adsorbent will be: $(\log 5 = 0.6990)$

Accepted Answer

The Freundlich adsorption isotherm is mathematically expressed as:$\dfrac xm = KP^{\cfrac1n}$It can be written in $y=mx+c$$\log\cfrac{x}{m}=\dfrac{1}{n}\times \log P+\log K$$\log\cfrac{x}{m}= \dfrac{1}{n}\log (0.5)+\log (10)$Therefore, plot of $log \dfrac{x}{m}$ vs $log\ P$ is a straight line with slope = $\dfrac{1}{n}$ and intercept = log KThus ,$\dfrac{1}{n} = tan&#952; = tan45^{0} =1 $$ n=1$$\log \cfrac{x}{m}=\log 5-\log (10)+\log (10)$$\log \cfrac{x}{m}=\log 5$$\cfrac{x}{m}=5$Hence amount of solute per gram is $5g$.

Question 9

For adsorption $\Delta G, \Delta S$ and $\Delta H$ all have negative values.

Accepted Answer

Adsorption is a spontaneous process accompanied by decrease in randomness.

Question 10

Adsorption of a gas follows Freundlich adsorption isotherm $x$ is the mass of the gas adsorbed on mass $m$ of the adsorbent. The plot of log $\dfrac{x}{m}$ versus log $p$ is shown in the given graph. $\dfrac{x}{m}$ is proportional to :

Accepted Answer

Solution:- (C) ${p}^{{2}/{3}}$$\dfrac{x}{m}=K.p^{1/n}$$\therefore log \dfrac{x}{m}=log K+\dfrac{1}{n}. log P$slope $=\dfrac{1}{n}=\dfrac{2}{3}$$\therefore \dfrac{x}{m}=K.p^{2/3}$

Revise with Concepts

Adsorption

Types of Adsorption

Adsorption Isotherms

Applications of Adsorption

Quick Summary With Stories

Introduction to Adsorption

Freundlich Adsorption Isotherm

Applications of Adsorption

What is an adsorption isotherm? Describe Freundlich adsorption isotherm?

Why does physisorption decrease with the increase of temperature?

Why is adsorption always exothermic?

What is the difference between physisorption and chemisorption?

According to Freundlich adsorption isotherm, which of the following is correct?

Distinguish between chemical and physical adsorption.

Which of the following is not characteristic of chemisorption?

The plot of $lo g x / m$ against $lo g p$ is a straight line inclined at an angle of $4 5^{\circ}$ . When the pressure is $0.5 a t m$ and Freundlich parameter, $k$ is $10$ , the amount of solute adsorbed per gram of adsorbent will be: $(lo g 5 = 0.6990)$

For adsorption $Δ G, Δ S$ and $Δ H$ all have negative values.

Adsorption is a spontaneous process accompanied by decrease in randomness.

Adsorption of a gas follows Freundlich adsorption isotherm $x$ is the mass of the gas adsorbed on mass $m$ of the adsorbent. The plot of log $\frac{x}{m}$ versus log $p$ is shown in the given graph. $\frac{x}{m}$ is proportional to :

Revise with Concepts

Adsorption

Types of Adsorption

Adsorption Isotherms

Applications of Adsorption

Quick Summary With Stories

Introduction to Adsorption

Freundlich Adsorption Isotherm

Applications of Adsorption

What is an adsorption isotherm? Describe Freundlich adsorption isotherm?

Why does physisorption decrease with the increase of temperature?

Why is adsorption always exothermic?

What is the difference between physisorption and chemisorption?

According to Freundlich adsorption isotherm, which of the following is correct?

Distinguish between chemical and physical adsorption.

Which of the following is not characteristic of chemisorption?

The plot oflogx/m against logp is a straight line inclined at an angle of 45∘. When the pressure is 0.5 atm and Freundlich parameter, k is 10, the amount of solute adsorbed per gram of adsorbent will be: (log5=0.6990)

For adsorption ΔG,ΔS and ΔH all have negative values.

Adsorption is a spontaneous process accompanied by decrease in randomness.

Adsorption of a gas follows Freundlich adsorption isotherm x is the mass of the gas adsorbed on mass m of the adsorbent. The plot of log mx​ versus log p is shown in the given graph. mx​ is proportional to :

The plot of $lo g x / m$ against $lo g p$ is a straight line inclined at an angle of $4 5^{\circ}$ . When the pressure is $0.5 a t m$ and Freundlich parameter, $k$ is $10$ , the amount of solute adsorbed per gram of adsorbent will be: $(lo g 5 = 0.6990)$

For adsorption $Δ G, Δ S$ and $Δ H$ all have negative values.

Adsorption of a gas follows Freundlich adsorption isotherm $x$ is the mass of the gas adsorbed on mass $m$ of the adsorbent. The plot of log $\frac{x}{m}$ versus log $p$ is shown in the given graph. $\frac{x}{m}$ is proportional to :