JEE Challenger
More from Surface Chemistry
ChemMedAdv 2017 • Paper 2

Analysis of Adsorption and Colloidal Phenomena Characteristics

Select the correct statement(s) pertaining to surface phenomena and colloidal properties:

Options

A

Adsorption is accompanied by a reduction in enthalpy together with a decrease in the system entropy.

Correct
B

Given the critical temperatures of ethane and nitrogen as 563 K563\text{ K} and 126 K126\text{ K} respectively, ethane exhibits greater adsorption than nitrogen on a fixed mass of activated charcoal under identical temperature conditions.

Correct
C

A cloud is categorized as an emulsion colloidal system having a liquid dispersed phase within a gaseous dispersion medium.

D

The Brownian movement of colloidal particles is unaffected by particle size, depending solely on the solution viscosity.

Topics & Concepts

Surface ChemistryAdsorptionColloids

Step-by-Step Solution

To determine the correct statements, let us analyze each option individually:

  1. Option [A]: Adsorption involves the accumulation of adsorbate molecules on the surface of an adsorbent, which forms attractive interactions and releases energy. Therefore, the process is exothermic: ΔH<0(decrease in enthalpy)\Delta H < 0 \quad (\text{decrease in enthalpy}) Furthermore, when gas or solute particles adhere to a surface, their degree of freedom and translational motion are restricted, leading to a decrease in randomness: ΔS<0(decrease in entropy of the system)\Delta S < 0 \quad (\text{decrease in entropy of the system}) For the process to be spontaneous (ΔG=ΔH−TΔS<0\Delta G = \Delta H - T\Delta S < 0), ΔH\Delta H must be negative to compensate for the unfavorable entropy change (−TΔS>0-T\Delta S > 0). Thus, statement [A] is correct.

  2. Option [B]: The extent of physical adsorption (physisorption) of a gas depends on the ease with which the gas can be liquefied, which is directly related to its critical temperature (TcT_c). A higher critical temperature indicates stronger intermolecular van der Waals forces of attraction. Given: Tc(ethane)=563 K>Tc(nitrogen)=126 KT_c(\text{ethane}) = 563\text{ K} > T_c(\text{nitrogen}) = 126\text{ K} Since Tc(ethane)>Tc(nitrogen)T_c(\text{ethane}) > T_c(\text{nitrogen}), ethane is more easily liquefiable and consequently adsorbs to a greater extent on activated charcoal than nitrogen under identical conditions. Thus, statement [B] is correct.

  3. Option [C]: A colloid consisting of a liquid dispersed phase in a gaseous dispersion medium is classified as a liquid aerosol (e.g., cloud, fog, mist). An emulsion is defined as a colloidal system where both the dispersed phase and the dispersion medium are immiscible liquids. Thus, statement [C] is incorrect.

  4. Option [D]: Brownian movement occurs due to the unbalanced bombardment of colloidal particles by the molecules of the dispersion medium. The rate/intensity of Brownian motion depends on:

    • Particle Size: Smaller particles experience greater net unbalanced forces and undergo more vigorous movement.
    • Viscosity: Lower viscosity of the dispersion medium permits faster movement.

    Since Brownian movement explicitly depends on particle size, statement [D] is incorrect.

Conclusion: The correct statements are A and B.

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